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When FRED is enabled, if the Trap Flag (TF) is set without an external debugger attached, it can lead to an infinite loop in the SIGTRAP handler. To avoid this, the software event flag in the augmented SS must be cleared, ensuring that no single-step trap remains pending when ERETU completes. This test checks for that specific scenario—verifying whether the kernel correctly prevents an infinite SIGTRAP loop in this edge case when FRED is enabled. The test should _always_ pass with IDT event delivery, thus no need to disable the test even when FRED is not enabled. Signed-off-by: Xin Li (Intel) <xin@zytor.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Tested-by: Sohil Mehta <sohil.mehta@intel.com> Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/20250609084054.2083189-3-xin%40zytor.com
101 lines
2.2 KiB
C
101 lines
2.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2025 Intel Corporation
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*/
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#define _GNU_SOURCE
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#include <err.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/ucontext.h>
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#ifdef __x86_64__
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# define REG_IP REG_RIP
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#else
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# define REG_IP REG_EIP
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#endif
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static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *), 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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return;
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}
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static void sigtrap(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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static unsigned int loop_count_on_same_ip;
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static unsigned long last_trap_ip;
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if (last_trap_ip == ctx->uc_mcontext.gregs[REG_IP]) {
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printf("\tTrapped at %016lx\n", last_trap_ip);
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/*
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* If the same IP is hit more than 10 times in a row, it is
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* _considered_ an infinite loop.
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*/
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if (++loop_count_on_same_ip > 10) {
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printf("[FAIL]\tDetected SIGTRAP infinite loop\n");
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exit(1);
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}
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return;
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}
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loop_count_on_same_ip = 0;
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last_trap_ip = ctx->uc_mcontext.gregs[REG_IP];
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printf("\tTrapped at %016lx\n", last_trap_ip);
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}
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int main(int argc, char *argv[])
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{
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sethandler(SIGTRAP, sigtrap, 0);
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/*
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* Set the Trap Flag (TF) to single-step the test code, therefore to
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* trigger a SIGTRAP signal after each instruction until the TF is
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* cleared.
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*
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* Because the arithmetic flags are not significant here, the TF is
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* set by pushing 0x302 onto the stack and then popping it into the
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* flags register.
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*
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* Four instructions in the following asm code are executed with the
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* TF set, thus the SIGTRAP handler is expected to run four times.
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*/
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printf("[RUN]\tSIGTRAP infinite loop detection\n");
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asm volatile(
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#ifdef __x86_64__
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/*
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* Avoid clobbering the redzone
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*
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* Equivalent to "sub $128, %rsp", however -128 can be encoded
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* in a single byte immediate while 128 uses 4 bytes.
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*/
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"add $-128, %rsp\n\t"
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#endif
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"push $0x302\n\t"
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"popf\n\t"
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"nop\n\t"
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"nop\n\t"
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"push $0x202\n\t"
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"popf\n\t"
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#ifdef __x86_64__
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"sub $-128, %rsp\n\t"
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#endif
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);
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printf("[OK]\tNo SIGTRAP infinite loop detected\n");
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return 0;
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}
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