[PATCH 3/5] selftests/x86: Add a test for signal frame portability
From: Andrei Vagin
Date: Tue May 26 2026 - 16:53:00 EST
Add a new selftest tools/testing/selftests/x86/sigframe_portability.c
that verifies that the kernel correctly restores the xstate context
even if the frame size has been manually reduced, as long as the
FP_XSTATE_MAGIC2 marker is correctly placed at the end of the
specified xstate_size.
This test simulates a scenario where a signal frame is created on a
system with fewer xstate features and restored on a system with more
features.
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
---
tools/testing/selftests/x86/Makefile | 5 +-
.../selftests/x86/sigframe_portability.c | 143 ++++++++++++++++++
tools/testing/selftests/x86/xstate.c | 5 -
tools/testing/selftests/x86/xstate.h | 7 +
4 files changed, 154 insertions(+), 6 deletions(-)
create mode 100644 tools/testing/selftests/x86/sigframe_portability.c
diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index 434065215d12..bd59ee3df61d 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -19,7 +19,8 @@ TARGETS_C_32BIT_ONLY := entry_from_vm86 test_syscall_vdso unwind_vdso \
test_FCMOV test_FCOMI test_FISTTP \
vdso_restorer
TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
- corrupt_xstate_header amx lam test_shadow_stack avx apx
+ corrupt_xstate_header amx lam test_shadow_stack avx apx \
+ sigframe_portability
# Some selftests require 32bit support enabled also on 64bit systems
TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall
@@ -138,3 +139,5 @@ $(OUTPUT)/avx_64: CFLAGS += -mno-avx -mno-avx512f
$(OUTPUT)/amx_64: EXTRA_FILES += xstate.c
$(OUTPUT)/avx_64: EXTRA_FILES += xstate.c
$(OUTPUT)/apx_64: EXTRA_FILES += xstate.c
+
+$(OUTPUT)/sigframe_portability_64: CFLAGS += -mno-avx -mno-avx512f
diff --git a/tools/testing/selftests/x86/sigframe_portability.c b/tools/testing/selftests/x86/sigframe_portability.c
new file mode 100644
index 000000000000..8888079a153a
--- /dev/null
+++ b/tools/testing/selftests/x86/sigframe_portability.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <signal.h>
+#include <string.h>
+#include <sys/ucontext.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <cpuid.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <asm/prctl.h>
+#include <stddef.h>
+
+#include "helpers.h"
+#include "xstate.h"
+
+/*
+ * This test verifies the portability of the signal frame.
+ * It simulates a scenario where a signal frame is created on a system with
+ * fewer xstate features and restored on a system with more features.
+ */
+
+#define SIGFRAME_XSTATE_HDR_OFFSET 512
+
+#define XSTATE_SSE_ONLY_SIZE (SIGFRAME_XSTATE_HDR_OFFSET + XSAVE_HDR_SIZE)
+#define XFEATURE_MASK_FPSSE ((1 << XFEATURE_FP) | (1 << XFEATURE_SSE))
+
+static uint32_t ymm_offset;
+static uint32_t xstate_size_ymm;
+
+/*
+ * Avoid using printf() in signal handlers as it is not
+ * async-signal-safe.
+ */
+#define SIGNAL_BUF_LEN 1024
+static char sig_err_buf[SIGNAL_BUF_LEN];
+
+static void check_avx_support(void)
+{
+ struct xstate_info xstate;
+
+ /* Check maximum supported CPUID leaf; we need 0xd for XSAVE */
+ if (get_xbuf_size() == 0)
+ ksft_exit_skip("XSAVE not supported\n");
+
+ xstate = get_xstate_info(XFEATURE_YMM);
+ if (!xstate.mask)
+ ksft_exit_skip("AVX not supported by hardware\n");
+
+ ymm_offset = xstate.xbuf_offset;
+ xstate_size_ymm = xstate.xbuf_offset + xstate.size;
+}
+
+#define TEST_YMMH_VAL (0x5656565656565656UL)
+
+static void handle_signal(int sig, siginfo_t *si, void *ucp)
+{
+ ucontext_t *uc = ucp;
+ void *fp = uc->uc_mcontext.fpregs;
+ struct _fpx_sw_bytes *sw = get_fpx_sw_bytes(fp);
+ struct xsave_buffer *xbuf;
+ uint64_t xfeatures, *ymmh_p;
+
+ if (sw->magic1 != FP_XSTATE_MAGIC1) {
+ snprintf(sig_err_buf, SIGNAL_BUF_LEN,
+ "magic1 is not valid: %x expected %x",
+ sw->magic1, FP_XSTATE_MAGIC1);
+ return;
+ }
+
+ xbuf = (struct xsave_buffer *)fp;
+
+ if (sw->xstate_size < xstate_size_ymm) {
+ snprintf(sig_err_buf, SIGNAL_BUF_LEN,
+ "xstate size is too small: %d (expected %d or greater)",
+ sw->xstate_size, xstate_size_ymm);
+ return;
+ }
+
+ sw->xstate_size = xstate_size_ymm;
+
+ xfeatures = get_xstatebv(xbuf);
+ xfeatures &= XFEATURE_MASK_FPSSE | (1 << XFEATURE_YMM);
+ set_xstatebv(xbuf, xfeatures);
+
+ *(uint32_t *)(fp + sw->xstate_size) = FP_XSTATE_MAGIC2;
+
+ ymmh_p = (uint64_t *)(fp + ymm_offset);
+ ymmh_p[0] = TEST_YMMH_VAL;
+ ymmh_p[1] = TEST_YMMH_VAL+1;
+
+ /* clear everything after MAGIC2. */
+ if (sw->xstate_size + 4 < sw->extended_size)
+ memset(fp + sw->xstate_size + 4, 0, sw->extended_size - sw->xstate_size - 4);
+}
+
+static void read_ymm0(uint64_t *v)
+{
+ asm volatile ("vmovdqu %%ymm0, %0" : "=m" (*(char (*)[32])v));
+}
+
+static void write_ymm0(uint64_t *v)
+{
+ asm volatile ("vmovdqu %0, %%ymm0" : : "m" (*(char (*)[32])v));
+}
+
+int main(void)
+{
+ uint64_t v[4] = {0, 0, 0, 0};
+
+ ksft_print_header();
+ ksft_set_plan(1);
+
+ check_avx_support();
+
+ sethandler(SIGUSR1, handle_signal, 0);
+
+ v[0] = 0x1111111111111111ULL;
+ v[1] = 0x2222222222222222ULL;
+ v[2] = 0x3333333333333333ULL;
+ v[3] = 0x4444444444444444ULL;
+ write_ymm0(v);
+
+ raise(SIGUSR1);
+ v[0] = v[1] = v[2] = v[3] = 0;
+ read_ymm0(v);
+
+ if (sig_err_buf[0])
+ ksft_test_result_fail("%s\n", sig_err_buf);
+ else if (v[2] == TEST_YMMH_VAL && v[3] == (TEST_YMMH_VAL + 1))
+ ksft_test_result_pass("YMM state restored correctly\n");
+ else
+ ksft_test_result_fail(
+ "Got upper bits: 0x%lx 0x%lx (expected %lx %lx)\n",
+ v[2], v[3], TEST_YMMH_VAL, TEST_YMMH_VAL + 1);
+
+ clearhandler(SIGUSR1);
+
+ ksft_finished();
+ return 0;
+}
diff --git a/tools/testing/selftests/x86/xstate.c b/tools/testing/selftests/x86/xstate.c
index 97fe4bd8bc77..40062b28c001 100644
--- a/tools/testing/selftests/x86/xstate.c
+++ b/tools/testing/selftests/x86/xstate.c
@@ -42,11 +42,6 @@ static inline uint64_t xgetbv(uint32_t index)
return eax + ((uint64_t)edx << 32);
}
-static inline uint64_t get_xstatebv(struct xsave_buffer *xbuf)
-{
- return *(uint64_t *)(&xbuf->header);
-}
-
static struct xstate_info xstate;
struct futex_info {
diff --git a/tools/testing/selftests/x86/xstate.h b/tools/testing/selftests/x86/xstate.h
index 6ee816e7625a..b24501b621f3 100644
--- a/tools/testing/selftests/x86/xstate.h
+++ b/tools/testing/selftests/x86/xstate.h
@@ -3,6 +3,8 @@
#define __SELFTESTS_X86_XSTATE_H
#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
#include "kselftest.h"
@@ -160,6 +162,11 @@ static inline void set_xstatebv(struct xsave_buffer *xbuf, uint64_t bv)
*(uint64_t *)(&xbuf->header) = bv;
}
+static inline uint64_t get_xstatebv(struct xsave_buffer *xbuf)
+{
+ return *(uint64_t *)(&xbuf->header);
+}
+
/* See 'struct _fpx_sw_bytes' at sigcontext.h */
#define SW_BYTES_OFFSET 464
/* N.B. The struct's field name varies so read from the offset. */
--
2.54.0.746.g67dd491aae-goog