[PATCH] x86_64: test xmm/ymm register state after execve(2)
From: Alexey Dobriyan
Date: Tue Dec 05 2023 - 09:21:10 EST
Test that xmm/ymm registers are cleared immediately after execve(2).
It is opportunistically named "check_xmm_ymm_zmm" because I don't have
AVX-512 machine but it will be trivial to extend without renaming stuff.
Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
---
I want to draw attention to executable sizes:
-rwxr-xr-x. 1 ad ad 723920 Dec 5 12:28 check_initial_reg_state_32
-rwxr-xr-x. 1 ad ad 825904 Dec 5 12:28 check_initial_reg_state_64
-rw-r--r--. 1 ad ad 1901 Dec 5 12:18 check_initial_reg_state.c
-rwxr-xr-x. 1 ad ad 827976 Dec 5 17:09 check_xmm_ymm_zmm_64
-rw-r--r--. 1 ad ad 4705 Dec 5 17:09 check_xmm_ymm_zmm.c
which are absolutely ridiculous!
These tests should fit into 1 page, both!
tools/testing/selftests/x86/Makefile | 2
tools/testing/selftests/x86/check_xmm_ymm_zmm.c | 176 ++++++++++++++++++++++++
2 files changed, 178 insertions(+)
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -20,6 +20,7 @@ TARGETS_C_32BIT_ONLY := entry_from_vm86 test_syscall_vdso unwind_vdso \
vdso_restorer
TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
corrupt_xstate_header amx lam test_shadow_stack
+TARGETS_C_64BIT_ONLY += check_xmm_ymm_zmm
# Some selftests require 32bit support enabled also on 64bit systems
TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall
@@ -110,6 +111,7 @@ $(OUTPUT)/test_syscall_vdso_32: thunks_32.S
# state.
$(OUTPUT)/check_initial_reg_state_32: CFLAGS += -Wl,-ereal_start -static
$(OUTPUT)/check_initial_reg_state_64: CFLAGS += -Wl,-ereal_start -static
+$(OUTPUT)/check_xmm_ymm_zmm_64: CFLAGS += -Wl,-ee_entry -static
$(OUTPUT)/nx_stack_32: CFLAGS += -Wl,-z,noexecstack
$(OUTPUT)/nx_stack_64: CFLAGS += -Wl,-z,noexecstack
new file mode 100644
--- /dev/null
+++ b/tools/testing/selftests/x86/check_xmm_ymm_zmm.c
@@ -0,0 +1,176 @@
+/*
+ * Copyright (c) 2023 Alexey Dobriyan <adobriyan@xxxxxxxxx>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test that xmm, ymm registers are cleared immediately after execve(2). */
+
+#include <stdio.h>
+#include <string.h>
+
+#if defined __amd64__
+#elif defined __i386__
+#error "fix register count, SSE2 detection"
+#else
+#error
+#endif
+
+#define array_size(a) (sizeof(a) / sizeof(a[0]))
+
+typedef char xmm_t[16];
+static const xmm_t xmm_z;
+static xmm_t xmm[16];
+
+typedef char ymm_t[32];
+static const ymm_t ymm_z;
+static ymm_t ymm[16];
+
+enum {
+ TEST_XMM = 1,
+ TEST_YMM = 2,
+};
+static volatile char g_test;
+
+/*
+ * Homework: write and install #UD handler in assembly and just start
+ * executing AVX-512/AVX2/SSE2 instructions falling back SIMD ladder
+ * if necessary.
+ *
+ * jk, use cpuid instead like any normal programmer would do.
+ */
+asm (
+".pushsection .text;"
+".type e_entry,@function;"
+".global e_entry;"
+"e_entry:"
+ /* test AVX2 support */
+ "mov $7, %eax;"
+ "xor %ecx, %ecx;"
+ "cpuid;"
+ "bt $5, %ebx;"
+ "jnc .Ltest_xmm;"
+
+ "vmovdqu %ymm0, ymm + 32 * 0;"
+ "vmovdqu %ymm1, ymm + 32 * 1;"
+ "vmovdqu %ymm2, ymm + 32 * 2;"
+ "vmovdqu %ymm3, ymm + 32 * 3;"
+ "vmovdqu %ymm4, ymm + 32 * 4;"
+ "vmovdqu %ymm5, ymm + 32 * 5;"
+ "vmovdqu %ymm6, ymm + 32 * 6;"
+ "vmovdqu %ymm7, ymm + 32 * 7;"
+ "vmovdqu %ymm8, ymm + 32 * 8;"
+ "vmovdqu %ymm9, ymm + 32 * 9;"
+ "vmovdqu %ymm10, ymm + 32 * 10;"
+ "vmovdqu %ymm11, ymm + 32 * 11;"
+ "vmovdqu %ymm12, ymm + 32 * 12;"
+ "vmovdqu %ymm13, ymm + 32 * 13;"
+ "vmovdqu %ymm14, ymm + 32 * 14;"
+ "vmovdqu %ymm15, ymm + 32 * 15;"
+ "movb $2, g_test;" /* TEST_YMM */
+ "jmp .Llibc_start;"
+
+".Ltest_xmm:"
+ "movdqu %xmm0, xmm + 16 * 0;"
+ "movdqu %xmm1, xmm + 16 * 1;"
+ "movdqu %xmm2, xmm + 16 * 2;"
+ "movdqu %xmm3, xmm + 16 * 3;"
+ "movdqu %xmm4, xmm + 16 * 4;"
+ "movdqu %xmm5, xmm + 16 * 5;"
+ "movdqu %xmm6, xmm + 16 * 6;"
+ "movdqu %xmm7, xmm + 16 * 7;"
+ "movdqu %xmm8, xmm + 16 * 8;"
+ "movdqu %xmm9, xmm + 16 * 9;"
+ "movdqu %xmm10, xmm + 16 * 10;"
+ "movdqu %xmm11, xmm + 16 * 11;"
+ "movdqu %xmm12, xmm + 16 * 12;"
+ "movdqu %xmm13, xmm + 16 * 13;"
+ "movdqu %xmm14, xmm + 16 * 14;"
+ "movdqu %xmm15, xmm + 16 * 15;"
+ "movb $1, g_test;" /* TEST_XMM */
+ "jmp .Llibc_start;"
+
+".Llibc_start:"
+ /*
+ * Undo cpuid, this is important for clean exit:
+ *
+ * Program received signal SIGSEGV, Segmentation fault.
+ * 0x0000000000000010 in ?? ()
+ * (gdb) bt
+ * #0 0x0000000000000010 in ?? ()
+ * #1 0x00000000004090c9 in __run_exit_handlers ()
+ * #2 0x0000000000409220 in exit ()
+ * #3 0x0000000000401da1 in __libc_start_call_main ()
+ * #4 0x00000000004034f0 in __libc_start_main_impl ()
+ * #5 0x0000000000401555 in _start ()
+ */
+ "xor %eax, %eax;"
+ "xor %ecx, %ecx;"
+ "xor %edx, %edx;"
+ "xor %ebx, %ebx;"
+ "jmp _start;"
+
+".size e_entry, .-e_entry;"
+".popsection;"
+);
+
+#define F stderr
+
+static void print_xymm(FILE *f, const char *pfx, const void *r, int len)
+{
+ fputs(pfx, f);
+ for (int i = 0; i < len; i += 1) {
+ fprintf(f, "%02hhx", *(unsigned char *)(r + i));
+ }
+ fputc('\n', f);
+}
+
+int main(void)
+{
+ int rv = 0;
+ if (g_test == TEST_YMM) {
+ for (int i = 0; i < array_size(ymm); i += 1) {
+ rv |= memcmp(&ymm[i], &ymm_z, sizeof(ymm_t)) != 0;
+ }
+ if (rv) {
+ fprintf(F, "FAIL\tymm\n");
+ for (int i = 0; i < array_size(ymm); i += 1) {
+ char buf[64];
+ snprintf(buf, sizeof(buf), "ymm%-2d = ", i);
+ print_xymm(F, buf, &ymm[i], sizeof(ymm_t));
+ }
+ return 1;
+ } else {
+ fprintf(F, "PASS\tymm0 .. ymm%zu == 0\n", array_size(ymm) - 1);
+ return 0;
+ }
+ } else if (g_test == TEST_XMM) {
+ for (int i = 0; i < array_size(xmm); i += 1) {
+ rv |= memcmp(&xmm[i], &xmm_z, sizeof(xmm_t)) != 0;
+ }
+ if (rv) {
+ fprintf(F, "FAIL\txmm\n");
+ for (int i = 0; i < array_size(xmm); i += 1) {
+ char buf[64];
+ snprintf(buf, sizeof(buf), "xmm%-2d = ", i);
+ print_xymm(F, buf, &xmm[i], sizeof(xmm_t));
+ }
+ return 1;
+ } else {
+ fprintf(F, "PASS\txmm0 .. xmm%zu == 0\n", array_size(xmm) - 1);
+ return 0;
+ }
+ } else {
+ fprintf(F, "FAIL\tg_test %d\n", +g_test);
+ return 1;
+ }
+}