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452 lines
10 KiB
452 lines
10 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* Copyright (C) 2020 ARM Ltd. |
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*/ |
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#include <linux/bitops.h> |
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#include <linux/kernel.h> |
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#include <linux/mm.h> |
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#include <linux/prctl.h> |
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#include <linux/sched.h> |
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#include <linux/sched/mm.h> |
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#include <linux/string.h> |
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#include <linux/swap.h> |
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#include <linux/swapops.h> |
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#include <linux/thread_info.h> |
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#include <linux/types.h> |
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#include <linux/uio.h> |
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#include <asm/barrier.h> |
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#include <asm/cpufeature.h> |
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#include <asm/mte.h> |
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#include <asm/ptrace.h> |
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#include <asm/sysreg.h> |
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u64 gcr_kernel_excl __ro_after_init; |
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static bool report_fault_once = true; |
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#ifdef CONFIG_KASAN_HW_TAGS |
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/* Whether the MTE asynchronous mode is enabled. */ |
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DEFINE_STATIC_KEY_FALSE(mte_async_mode); |
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EXPORT_SYMBOL_GPL(mte_async_mode); |
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#endif |
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static void mte_sync_page_tags(struct page *page, pte_t old_pte, |
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bool check_swap, bool pte_is_tagged) |
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{ |
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if (check_swap && is_swap_pte(old_pte)) { |
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swp_entry_t entry = pte_to_swp_entry(old_pte); |
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if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) |
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return; |
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} |
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if (!pte_is_tagged) |
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return; |
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page_kasan_tag_reset(page); |
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/* |
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* We need smp_wmb() in between setting the flags and clearing the |
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* tags because if another thread reads page->flags and builds a |
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* tagged address out of it, there is an actual dependency to the |
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* memory access, but on the current thread we do not guarantee that |
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* the new page->flags are visible before the tags were updated. |
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*/ |
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smp_wmb(); |
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mte_clear_page_tags(page_address(page)); |
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} |
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void mte_sync_tags(pte_t old_pte, pte_t pte) |
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{ |
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struct page *page = pte_page(pte); |
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long i, nr_pages = compound_nr(page); |
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bool check_swap = nr_pages == 1; |
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bool pte_is_tagged = pte_tagged(pte); |
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/* Early out if there's nothing to do */ |
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if (!check_swap && !pte_is_tagged) |
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return; |
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/* if PG_mte_tagged is set, tags have already been initialised */ |
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for (i = 0; i < nr_pages; i++, page++) { |
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if (!test_and_set_bit(PG_mte_tagged, &page->flags)) |
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mte_sync_page_tags(page, old_pte, check_swap, |
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pte_is_tagged); |
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} |
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} |
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int memcmp_pages(struct page *page1, struct page *page2) |
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{ |
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char *addr1, *addr2; |
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int ret; |
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addr1 = page_address(page1); |
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addr2 = page_address(page2); |
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ret = memcmp(addr1, addr2, PAGE_SIZE); |
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if (!system_supports_mte() || ret) |
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return ret; |
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/* |
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* If the page content is identical but at least one of the pages is |
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* tagged, return non-zero to avoid KSM merging. If only one of the |
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* pages is tagged, set_pte_at() may zero or change the tags of the |
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* other page via mte_sync_tags(). |
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*/ |
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if (test_bit(PG_mte_tagged, &page1->flags) || |
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test_bit(PG_mte_tagged, &page2->flags)) |
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return addr1 != addr2; |
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return ret; |
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} |
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void mte_init_tags(u64 max_tag) |
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{ |
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static bool gcr_kernel_excl_initialized; |
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if (!gcr_kernel_excl_initialized) { |
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/* |
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* The format of the tags in KASAN is 0xFF and in MTE is 0xF. |
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* This conversion extracts an MTE tag from a KASAN tag. |
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*/ |
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u64 incl = GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT, |
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max_tag), 0); |
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gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK; |
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gcr_kernel_excl_initialized = true; |
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} |
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/* Enable the kernel exclude mask for random tags generation. */ |
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write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1); |
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} |
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static inline void __mte_enable_kernel(const char *mode, unsigned long tcf) |
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{ |
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/* Enable MTE Sync Mode for EL1. */ |
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sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf); |
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isb(); |
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pr_info_once("MTE: enabled in %s mode at EL1\n", mode); |
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} |
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#ifdef CONFIG_KASAN_HW_TAGS |
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void mte_enable_kernel_sync(void) |
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{ |
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/* |
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* Make sure we enter this function when no PE has set |
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* async mode previously. |
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*/ |
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WARN_ONCE(system_uses_mte_async_mode(), |
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"MTE async mode enabled system wide!"); |
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__mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC); |
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} |
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void mte_enable_kernel_async(void) |
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{ |
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__mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC); |
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/* |
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* MTE async mode is set system wide by the first PE that |
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* executes this function. |
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* |
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* Note: If in future KASAN acquires a runtime switching |
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* mode in between sync and async, this strategy needs |
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* to be reviewed. |
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*/ |
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if (!system_uses_mte_async_mode()) |
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static_branch_enable(&mte_async_mode); |
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} |
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#endif |
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void mte_set_report_once(bool state) |
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{ |
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WRITE_ONCE(report_fault_once, state); |
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} |
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bool mte_report_once(void) |
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{ |
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return READ_ONCE(report_fault_once); |
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} |
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#ifdef CONFIG_KASAN_HW_TAGS |
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void mte_check_tfsr_el1(void) |
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{ |
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u64 tfsr_el1; |
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if (!system_supports_mte()) |
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return; |
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tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1); |
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if (unlikely(tfsr_el1 & SYS_TFSR_EL1_TF1)) { |
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/* |
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* Note: isb() is not required after this direct write |
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* because there is no indirect read subsequent to it |
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* (per ARM DDI 0487F.c table D13-1). |
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*/ |
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write_sysreg_s(0, SYS_TFSR_EL1); |
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kasan_report_async(); |
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} |
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} |
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#endif |
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static void set_gcr_el1_excl(u64 excl) |
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{ |
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current->thread.gcr_user_excl = excl; |
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/* |
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* SYS_GCR_EL1 will be set to current->thread.gcr_user_excl value |
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* by mte_set_user_gcr() in kernel_exit, |
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*/ |
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} |
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void mte_thread_init_user(void) |
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{ |
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if (!system_supports_mte()) |
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return; |
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/* clear any pending asynchronous tag fault */ |
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dsb(ish); |
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write_sysreg_s(0, SYS_TFSRE0_EL1); |
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clear_thread_flag(TIF_MTE_ASYNC_FAULT); |
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/* disable tag checking */ |
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set_task_sctlr_el1((current->thread.sctlr_user & ~SCTLR_EL1_TCF0_MASK) | |
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SCTLR_EL1_TCF0_NONE); |
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/* reset tag generation mask */ |
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set_gcr_el1_excl(SYS_GCR_EL1_EXCL_MASK); |
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} |
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void mte_thread_switch(struct task_struct *next) |
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{ |
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/* |
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* Check if an async tag exception occurred at EL1. |
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* |
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* Note: On the context switch path we rely on the dsb() present |
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* in __switch_to() to guarantee that the indirect writes to TFSR_EL1 |
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* are synchronized before this point. |
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*/ |
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isb(); |
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mte_check_tfsr_el1(); |
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} |
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void mte_suspend_enter(void) |
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{ |
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if (!system_supports_mte()) |
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return; |
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/* |
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* The barriers are required to guarantee that the indirect writes |
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* to TFSR_EL1 are synchronized before we report the state. |
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*/ |
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dsb(nsh); |
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isb(); |
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/* Report SYS_TFSR_EL1 before suspend entry */ |
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mte_check_tfsr_el1(); |
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} |
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void mte_suspend_exit(void) |
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{ |
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if (!system_supports_mte()) |
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return; |
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sysreg_clear_set_s(SYS_GCR_EL1, SYS_GCR_EL1_EXCL_MASK, gcr_kernel_excl); |
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isb(); |
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} |
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long set_mte_ctrl(struct task_struct *task, unsigned long arg) |
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{ |
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u64 sctlr = task->thread.sctlr_user & ~SCTLR_EL1_TCF0_MASK; |
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u64 gcr_excl = ~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) & |
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SYS_GCR_EL1_EXCL_MASK; |
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if (!system_supports_mte()) |
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return 0; |
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switch (arg & PR_MTE_TCF_MASK) { |
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case PR_MTE_TCF_NONE: |
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sctlr |= SCTLR_EL1_TCF0_NONE; |
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break; |
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case PR_MTE_TCF_SYNC: |
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sctlr |= SCTLR_EL1_TCF0_SYNC; |
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break; |
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case PR_MTE_TCF_ASYNC: |
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sctlr |= SCTLR_EL1_TCF0_ASYNC; |
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break; |
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default: |
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return -EINVAL; |
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} |
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if (task != current) { |
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task->thread.sctlr_user = sctlr; |
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task->thread.gcr_user_excl = gcr_excl; |
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} else { |
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set_task_sctlr_el1(sctlr); |
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set_gcr_el1_excl(gcr_excl); |
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} |
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return 0; |
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} |
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long get_mte_ctrl(struct task_struct *task) |
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{ |
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unsigned long ret; |
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u64 incl = ~task->thread.gcr_user_excl & SYS_GCR_EL1_EXCL_MASK; |
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if (!system_supports_mte()) |
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return 0; |
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ret = incl << PR_MTE_TAG_SHIFT; |
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switch (task->thread.sctlr_user & SCTLR_EL1_TCF0_MASK) { |
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case SCTLR_EL1_TCF0_NONE: |
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ret |= PR_MTE_TCF_NONE; |
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break; |
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case SCTLR_EL1_TCF0_SYNC: |
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ret |= PR_MTE_TCF_SYNC; |
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break; |
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case SCTLR_EL1_TCF0_ASYNC: |
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ret |= PR_MTE_TCF_ASYNC; |
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break; |
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} |
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return ret; |
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} |
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/* |
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* Access MTE tags in another process' address space as given in mm. Update |
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* the number of tags copied. Return 0 if any tags copied, error otherwise. |
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* Inspired by __access_remote_vm(). |
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*/ |
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static int __access_remote_tags(struct mm_struct *mm, unsigned long addr, |
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struct iovec *kiov, unsigned int gup_flags) |
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{ |
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struct vm_area_struct *vma; |
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void __user *buf = kiov->iov_base; |
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size_t len = kiov->iov_len; |
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int ret; |
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int write = gup_flags & FOLL_WRITE; |
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if (!access_ok(buf, len)) |
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return -EFAULT; |
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if (mmap_read_lock_killable(mm)) |
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return -EIO; |
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while (len) { |
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unsigned long tags, offset; |
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void *maddr; |
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struct page *page = NULL; |
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ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page, |
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&vma, NULL); |
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if (ret <= 0) |
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break; |
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/* |
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* Only copy tags if the page has been mapped as PROT_MTE |
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* (PG_mte_tagged set). Otherwise the tags are not valid and |
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* not accessible to user. Moreover, an mprotect(PROT_MTE) |
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* would cause the existing tags to be cleared if the page |
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* was never mapped with PROT_MTE. |
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*/ |
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if (!(vma->vm_flags & VM_MTE)) { |
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ret = -EOPNOTSUPP; |
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put_page(page); |
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break; |
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} |
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WARN_ON_ONCE(!test_bit(PG_mte_tagged, &page->flags)); |
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/* limit access to the end of the page */ |
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offset = offset_in_page(addr); |
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tags = min(len, (PAGE_SIZE - offset) / MTE_GRANULE_SIZE); |
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maddr = page_address(page); |
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if (write) { |
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tags = mte_copy_tags_from_user(maddr + offset, buf, tags); |
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set_page_dirty_lock(page); |
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} else { |
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tags = mte_copy_tags_to_user(buf, maddr + offset, tags); |
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} |
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put_page(page); |
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/* error accessing the tracer's buffer */ |
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if (!tags) |
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break; |
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len -= tags; |
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buf += tags; |
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addr += tags * MTE_GRANULE_SIZE; |
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} |
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mmap_read_unlock(mm); |
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/* return an error if no tags copied */ |
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kiov->iov_len = buf - kiov->iov_base; |
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if (!kiov->iov_len) { |
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/* check for error accessing the tracee's address space */ |
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if (ret <= 0) |
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return -EIO; |
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else |
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return -EFAULT; |
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} |
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return 0; |
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} |
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/* |
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* Copy MTE tags in another process' address space at 'addr' to/from tracer's |
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* iovec buffer. Return 0 on success. Inspired by ptrace_access_vm(). |
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*/ |
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static int access_remote_tags(struct task_struct *tsk, unsigned long addr, |
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struct iovec *kiov, unsigned int gup_flags) |
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{ |
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struct mm_struct *mm; |
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int ret; |
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mm = get_task_mm(tsk); |
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if (!mm) |
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return -EPERM; |
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if (!tsk->ptrace || (current != tsk->parent) || |
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((get_dumpable(mm) != SUID_DUMP_USER) && |
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!ptracer_capable(tsk, mm->user_ns))) { |
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mmput(mm); |
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return -EPERM; |
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} |
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ret = __access_remote_tags(mm, addr, kiov, gup_flags); |
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mmput(mm); |
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return ret; |
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} |
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int mte_ptrace_copy_tags(struct task_struct *child, long request, |
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unsigned long addr, unsigned long data) |
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{ |
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int ret; |
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struct iovec kiov; |
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struct iovec __user *uiov = (void __user *)data; |
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unsigned int gup_flags = FOLL_FORCE; |
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if (!system_supports_mte()) |
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return -EIO; |
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if (get_user(kiov.iov_base, &uiov->iov_base) || |
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get_user(kiov.iov_len, &uiov->iov_len)) |
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return -EFAULT; |
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if (request == PTRACE_POKEMTETAGS) |
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gup_flags |= FOLL_WRITE; |
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/* align addr to the MTE tag granule */ |
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addr &= MTE_GRANULE_MASK; |
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ret = access_remote_tags(child, addr, &kiov, gup_flags); |
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if (!ret) |
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ret = put_user(kiov.iov_len, &uiov->iov_len); |
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return ret; |
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}
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