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kselftest: arm64: Check access to GCS after mprotect(PROT_NONE)

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A GCS mapping should not be accessible after mprotect(PROT_NONE). Add a
kselftest for this scenario.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Catalin Marinas 2026-02-23 17:45:32 +00:00 • committed by Will Deacon
parent 47a8aad135
commit 9d1a7c4a45
1 changed files with 76 additions and 0 deletions
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76
tools/testing/selftests/arm64/signal/testcases/gcs_prot_none_fault.c Normal file
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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2026 ARM Limited
*/
#include <errno.h>
#include <signal.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include "test_signals_utils.h"
#include "testcases.h"
static uint64_t *gcs_page;
static bool post_mprotect;
#ifndef __NR_map_shadow_stack
#define __NR_map_shadow_stack 453
#endif
static bool alloc_gcs(struct tdescr *td)
{
long page_size = sysconf(_SC_PAGE_SIZE);
gcs_page = (void *)syscall(__NR_map_shadow_stack, 0,
page_size, 0);
if (gcs_page == MAP_FAILED) {
fprintf(stderr, "Failed to map %ld byte GCS: %d\n",
page_size, errno);
return false;
}
return true;
}
static int gcs_prot_none_fault_trigger(struct tdescr *td)
{
/* Verify that the page is readable (ie, not completely unmapped) */
fprintf(stderr, "Read value 0x%lx\n", gcs_page[0]);
if (mprotect(gcs_page, sysconf(_SC_PAGE_SIZE), PROT_NONE) != 0) {
fprintf(stderr, "mprotect(PROT_NONE) failed: %d\n", errno);
return 0;
}
post_mprotect = true;
/* This should trigger a fault if PROT_NONE is honoured for the GCS page */
fprintf(stderr, "Read value after mprotect(PROT_NONE) 0x%lx\n", gcs_page[0]);
return 0;
}
static int gcs_prot_none_fault_signal(struct tdescr *td, siginfo_t *si,
ucontext_t *uc)
{
ASSERT_GOOD_CONTEXT(uc);
/* A fault before mprotect(PROT_NONE) is unexpected. */
if (!post_mprotect)
return 0;
return 1;
}
struct tdescr tde = {
.name = "GCS PROT_NONE fault",
.descr = "Read from GCS after mprotect(PROT_NONE) segfaults",
.feats_required = FEAT_GCS,
.timeout = 3,
.sig_ok = SIGSEGV,
.sanity_disabled = true,
.init = alloc_gcs,
.trigger = gcs_prot_none_fault_trigger,
.run = gcs_prot_none_fault_signal,
};