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187 lines
4.4 KiB
187 lines
4.4 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* sigreturn.c - tests that x86 avoids Intel SYSRET pitfalls |
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* Copyright (c) 2014-2016 Andrew Lutomirski |
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*/ |
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#define _GNU_SOURCE |
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#include <stdlib.h> |
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#include <unistd.h> |
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#include <stdio.h> |
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#include <string.h> |
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#include <inttypes.h> |
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#include <sys/signal.h> |
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#include <sys/ucontext.h> |
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#include <sys/syscall.h> |
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#include <err.h> |
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#include <stddef.h> |
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#include <stdbool.h> |
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#include <setjmp.h> |
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#include <sys/user.h> |
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#include <sys/mman.h> |
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#include <assert.h> |
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asm ( |
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".pushsection \".text\", \"ax\"\n\t" |
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".balign 4096\n\t" |
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"test_page: .globl test_page\n\t" |
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".fill 4094,1,0xcc\n\t" |
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"test_syscall_insn:\n\t" |
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"syscall\n\t" |
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".ifne . - test_page - 4096\n\t" |
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".error \"test page is not one page long\"\n\t" |
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".endif\n\t" |
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".popsection" |
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); |
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extern const char test_page[]; |
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static void const *current_test_page_addr = test_page; |
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static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *), |
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int flags) |
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{ |
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struct sigaction sa; |
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memset(&sa, 0, sizeof(sa)); |
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sa.sa_sigaction = handler; |
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sa.sa_flags = SA_SIGINFO | flags; |
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sigemptyset(&sa.sa_mask); |
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if (sigaction(sig, &sa, 0)) |
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err(1, "sigaction"); |
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} |
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static void clearhandler(int sig) |
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{ |
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struct sigaction sa; |
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memset(&sa, 0, sizeof(sa)); |
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sa.sa_handler = SIG_DFL; |
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sigemptyset(&sa.sa_mask); |
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if (sigaction(sig, &sa, 0)) |
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err(1, "sigaction"); |
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} |
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/* State used by our signal handlers. */ |
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static gregset_t initial_regs; |
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static volatile unsigned long rip; |
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static void sigsegv_for_sigreturn_test(int sig, siginfo_t *info, void *ctx_void) |
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{ |
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ucontext_t *ctx = (ucontext_t*)ctx_void; |
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if (rip != ctx->uc_mcontext.gregs[REG_RIP]) { |
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printf("[FAIL]\tRequested RIP=0x%lx but got RIP=0x%lx\n", |
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rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]); |
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fflush(stdout); |
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_exit(1); |
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} |
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memcpy(&ctx->uc_mcontext.gregs, &initial_regs, sizeof(gregset_t)); |
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printf("[OK]\tGot SIGSEGV at RIP=0x%lx\n", rip); |
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} |
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static void sigusr1(int sig, siginfo_t *info, void *ctx_void) |
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{ |
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ucontext_t *ctx = (ucontext_t*)ctx_void; |
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memcpy(&initial_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t)); |
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/* Set IP and CX to match so that SYSRET can happen. */ |
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ctx->uc_mcontext.gregs[REG_RIP] = rip; |
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ctx->uc_mcontext.gregs[REG_RCX] = rip; |
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/* R11 and EFLAGS should already match. */ |
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assert(ctx->uc_mcontext.gregs[REG_EFL] == |
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ctx->uc_mcontext.gregs[REG_R11]); |
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sethandler(SIGSEGV, sigsegv_for_sigreturn_test, SA_RESETHAND); |
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return; |
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} |
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static void test_sigreturn_to(unsigned long ip) |
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{ |
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rip = ip; |
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printf("[RUN]\tsigreturn to 0x%lx\n", ip); |
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raise(SIGUSR1); |
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} |
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static jmp_buf jmpbuf; |
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static void sigsegv_for_fallthrough(int sig, siginfo_t *info, void *ctx_void) |
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{ |
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ucontext_t *ctx = (ucontext_t*)ctx_void; |
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if (rip != ctx->uc_mcontext.gregs[REG_RIP]) { |
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printf("[FAIL]\tExpected SIGSEGV at 0x%lx but got RIP=0x%lx\n", |
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rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]); |
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fflush(stdout); |
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_exit(1); |
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} |
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siglongjmp(jmpbuf, 1); |
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} |
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static void test_syscall_fallthrough_to(unsigned long ip) |
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{ |
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void *new_address = (void *)(ip - 4096); |
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void *ret; |
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printf("[RUN]\tTrying a SYSCALL that falls through to 0x%lx\n", ip); |
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ret = mremap((void *)current_test_page_addr, 4096, 4096, |
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MREMAP_MAYMOVE | MREMAP_FIXED, new_address); |
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if (ret == MAP_FAILED) { |
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if (ip <= (1UL << 47) - PAGE_SIZE) { |
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err(1, "mremap to %p", new_address); |
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} else { |
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printf("[OK]\tmremap to %p failed\n", new_address); |
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return; |
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} |
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} |
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if (ret != new_address) |
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errx(1, "mremap malfunctioned: asked for %p but got %p\n", |
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new_address, ret); |
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current_test_page_addr = new_address; |
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rip = ip; |
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if (sigsetjmp(jmpbuf, 1) == 0) { |
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asm volatile ("call *%[syscall_insn]" :: "a" (SYS_getpid), |
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[syscall_insn] "rm" (ip - 2)); |
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errx(1, "[FAIL]\tSyscall trampoline returned"); |
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} |
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printf("[OK]\tWe survived\n"); |
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} |
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int main() |
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{ |
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/* |
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* When the kernel returns from a slow-path syscall, it will |
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* detect whether SYSRET is appropriate. If it incorrectly |
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* thinks that SYSRET is appropriate when RIP is noncanonical, |
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* it'll crash on Intel CPUs. |
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*/ |
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sethandler(SIGUSR1, sigusr1, 0); |
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for (int i = 47; i < 64; i++) |
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test_sigreturn_to(1UL<<i); |
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clearhandler(SIGUSR1); |
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sethandler(SIGSEGV, sigsegv_for_fallthrough, 0); |
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/* One extra test to check that we didn't screw up the mremap logic. */ |
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test_syscall_fallthrough_to((1UL << 47) - 2*PAGE_SIZE); |
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/* These are the interesting cases. */ |
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for (int i = 47; i < 64; i++) { |
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test_syscall_fallthrough_to((1UL<<i) - PAGE_SIZE); |
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test_syscall_fallthrough_to(1UL<<i); |
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} |
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return 0; |
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}
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