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110 lines
2.9 KiB
110 lines
2.9 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* memconsole-coreboot.c |
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* |
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* Memory based BIOS console accessed through coreboot table. |
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* |
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* Copyright 2017 Google Inc. |
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*/ |
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#include <linux/device.h> |
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#include <linux/io.h> |
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#include <linux/kernel.h> |
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#include <linux/module.h> |
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#include "memconsole.h" |
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#include "coreboot_table.h" |
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#define CB_TAG_CBMEM_CONSOLE 0x17 |
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/* CBMEM firmware console log descriptor. */ |
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struct cbmem_cons { |
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u32 size_dont_access_after_boot; |
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u32 cursor; |
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u8 body[]; |
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} __packed; |
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#define CURSOR_MASK ((1 << 28) - 1) |
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#define OVERFLOW (1 << 31) |
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static struct cbmem_cons *cbmem_console; |
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static u32 cbmem_console_size; |
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/* |
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* The cbmem_console structure is read again on every access because it may |
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* change at any time if runtime firmware logs new messages. This may rarely |
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* lead to race conditions where the firmware overwrites the beginning of the |
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* ring buffer with more lines after we have already read |cursor|. It should be |
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* rare and harmless enough that we don't spend extra effort working around it. |
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*/ |
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static ssize_t memconsole_coreboot_read(char *buf, loff_t pos, size_t count) |
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{ |
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u32 cursor = cbmem_console->cursor & CURSOR_MASK; |
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u32 flags = cbmem_console->cursor & ~CURSOR_MASK; |
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u32 size = cbmem_console_size; |
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struct seg { /* describes ring buffer segments in logical order */ |
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u32 phys; /* physical offset from start of mem buffer */ |
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u32 len; /* length of segment */ |
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} seg[2] = { {0}, {0} }; |
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size_t done = 0; |
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int i; |
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if (flags & OVERFLOW) { |
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if (cursor > size) /* Shouldn't really happen, but... */ |
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cursor = 0; |
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seg[0] = (struct seg){.phys = cursor, .len = size - cursor}; |
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seg[1] = (struct seg){.phys = 0, .len = cursor}; |
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} else { |
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seg[0] = (struct seg){.phys = 0, .len = min(cursor, size)}; |
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} |
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for (i = 0; i < ARRAY_SIZE(seg) && count > done; i++) { |
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done += memory_read_from_buffer(buf + done, count - done, &pos, |
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cbmem_console->body + seg[i].phys, seg[i].len); |
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pos -= seg[i].len; |
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} |
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return done; |
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} |
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static int memconsole_probe(struct coreboot_device *dev) |
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{ |
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struct cbmem_cons *tmp_cbmc; |
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tmp_cbmc = memremap(dev->cbmem_ref.cbmem_addr, |
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sizeof(*tmp_cbmc), MEMREMAP_WB); |
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if (!tmp_cbmc) |
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return -ENOMEM; |
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/* Read size only once to prevent overrun attack through /dev/mem. */ |
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cbmem_console_size = tmp_cbmc->size_dont_access_after_boot; |
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cbmem_console = devm_memremap(&dev->dev, dev->cbmem_ref.cbmem_addr, |
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cbmem_console_size + sizeof(*cbmem_console), |
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MEMREMAP_WB); |
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memunmap(tmp_cbmc); |
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if (IS_ERR(cbmem_console)) |
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return PTR_ERR(cbmem_console); |
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memconsole_setup(memconsole_coreboot_read); |
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return memconsole_sysfs_init(); |
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} |
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static void memconsole_remove(struct coreboot_device *dev) |
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{ |
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memconsole_exit(); |
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} |
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static struct coreboot_driver memconsole_driver = { |
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.probe = memconsole_probe, |
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.remove = memconsole_remove, |
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.drv = { |
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.name = "memconsole", |
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}, |
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.tag = CB_TAG_CBMEM_CONSOLE, |
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}; |
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module_coreboot_driver(memconsole_driver); |
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MODULE_AUTHOR("Google, Inc."); |
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MODULE_LICENSE("GPL");
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