Commit 9d1a7c4a authored by Catalin Marinas's avatar Catalin Marinas Committed by Will Deacon
Browse files

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



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

Signed-off-by: default avatarCatalin 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: default avatarMark Brown <broonie@kernel.org>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 47a8aad1

tools/testing/selftests/arm64/signal/testcases/gcs_prot_none_fault.c

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+76 −0
Original line number Diff line number Diff line 
// 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,

};