selftests/x86/xstate: Refactor ptrace ABI test

Following the refactoring of the context switching test, the ptrace test is
another component reusable for other xstate features. As part of this
restructuring, add a missing check to validate the
user_xstateregs->xstate_fx_sw field in the ABI.

Also, replace err() and fatal_error() with ksft_exit_fail_msg() for
consistency in error handling.

  Expected output:
  $ amx_64
  ...
  [RUN]   AMX Tile data: inject xstate via ptrace().
  [OK]    'xfeatures' in SW reserved area was correctly written
  [OK]    xstate was correctly updated.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250226010731.2456-6-chang.seok.bae@intel.com

Author: ChangSeokBae

tools/testing/selftests/x86/amx.c

@@ -13,10 +13,8 @@
 #include <sys/auxv.h>
 #include <sys/mman.h>
 #include <sys/shm.h>
-#include <sys/ptrace.h>
 #include <sys/syscall.h>
 #include <sys/wait.h>
-#include <sys/uio.h>
 
 #include "helpers.h"
 #include "xstate.h"
@@ -32,8 +30,6 @@
 #define XFEATURE_MASK_XTILEDATA	(1 << XFEATURE_XTILEDATA)
 #define XFEATURE_MASK_XTILE	(XFEATURE_MASK_XTILECFG | XFEATURE_MASK_XTILEDATA)
 
-static uint32_t xbuf_size;
-
 struct xstate_info xtiledata;
 
 /* The helpers for managing XSAVE buffer and tile states: */
@@ -154,13 +150,6 @@ static inline bool load_rand_tiledata(struct xsave_buffer *xbuf)
 	return xrstor_safe(xbuf, XFEATURE_MASK_XTILEDATA);
 }
 
-/* Return XTILEDATA to its initial configuration. */
-static inline void init_xtiledata(void)
-{
-	clear_xstate_header(stashed_xsave);
-	xrstor_safe(stashed_xsave, XFEATURE_MASK_XTILEDATA);
-}
-
 enum expected_result { FAIL_EXPECTED, SUCCESS_EXPECTED };
 
 /* arch_prctl() and sigaltstack() test */
@@ -489,99 +478,6 @@ static void test_fork(void)
 	_exit(0);
 }
 
-/* Ptrace test */
-
-/*
- * Make sure the ptracee has the expanded kernel buffer on the first
- * use. Then, initialize the state before performing the state
- * injection from the ptracer.
- */
-static inline void ptracee_firstuse_tiledata(void)
-{
-	load_rand_tiledata(stashed_xsave);
-	init_xtiledata();
-}
-
-/*
- * Ptracer injects the randomized tile data state. It also reads
- * before and after that, which will execute the kernel's state copy
- * functions. So, the tester is advised to double-check any emitted
- * kernel messages.
- */
-static void ptracer_inject_tiledata(pid_t target)
-{
-	struct xsave_buffer *xbuf;
-	struct iovec iov;
-
-	xbuf = alloc_xbuf();
-	if (!xbuf)
-		fatal_error("unable to allocate XSAVE buffer");
-
-	printf("\tRead the init'ed tiledata via ptrace().\n");
-
-	iov.iov_base = xbuf;
-	iov.iov_len = xbuf_size;
-
-	memset(stashed_xsave, 0, xbuf_size);
-
-	if (ptrace(PTRACE_GETREGSET, target, (uint32_t)NT_X86_XSTATE, &iov))
-		fatal_error("PTRACE_GETREGSET");
-
-	if (!__compare_tiledata_state(stashed_xsave, xbuf))
-		printf("[OK]\tThe init'ed tiledata was read from ptracee.\n");
-	else
-		printf("[FAIL]\tThe init'ed tiledata was not read from ptracee.\n");
-
-	printf("\tInject tiledata via ptrace().\n");
-
-	load_rand_tiledata(xbuf);
-
-	memcpy(&stashed_xsave->bytes[xtiledata.xbuf_offset],
-	       &xbuf->bytes[xtiledata.xbuf_offset],
-	       xtiledata.size);
-
-	if (ptrace(PTRACE_SETREGSET, target, (uint32_t)NT_X86_XSTATE, &iov))
-		fatal_error("PTRACE_SETREGSET");
-
-	if (ptrace(PTRACE_GETREGSET, target, (uint32_t)NT_X86_XSTATE, &iov))
-		fatal_error("PTRACE_GETREGSET");
-
-	if (!__compare_tiledata_state(stashed_xsave, xbuf))
-		printf("[OK]\tTiledata was correctly written to ptracee.\n");
-	else
-		printf("[FAIL]\tTiledata was not correctly written to ptracee.\n");
-}
-
-static void test_ptrace(void)
-{
-	pid_t child;
-	int status;
-
-	child = fork();
-	if (child < 0) {
-		err(1, "fork");
-	} else if (!child) {
-		if (ptrace(PTRACE_TRACEME, 0, NULL, NULL))
-			err(1, "PTRACE_TRACEME");
-
-		ptracee_firstuse_tiledata();
-
-		raise(SIGTRAP);
-		_exit(0);
-	}
-
-	do {
-		wait(&status);
-	} while (WSTOPSIG(status) != SIGTRAP);
-
-	ptracer_inject_tiledata(child);
-
-	ptrace(PTRACE_DETACH, child, NULL, NULL);
-	wait(&status);
-	if (!WIFEXITED(status) || WEXITSTATUS(status))
-		err(1, "ptrace test");
-}
-
 int main(void)
 {
 	const unsigned int ctxtsw_num_threads = 5, ctxtsw_iterations = 10;
@@ -594,8 +490,6 @@ int main(void)
 		return KSFT_SKIP;
 	}
 
-	xbuf_size = get_xbuf_size();
-
 	xtiledata = get_xstate_info(XFEATURE_XTILEDATA);
 	if (!xtiledata.size || !xtiledata.xbuf_offset) {
 		fatal_error("xstate cpuid: invalid tile data size/offset: %d/%d",
@@ -614,7 +508,7 @@ int main(void)
 
 	test_context_switch(XFEATURE_XTILEDATA, ctxtsw_num_threads, ctxtsw_iterations);
 
-	test_ptrace();
+	test_ptrace(XFEATURE_XTILEDATA);
 
 	clearhandler(SIGILL);
 	free_stashed_xsave();

tools/testing/selftests/x86/xstate.c

@@ -2,12 +2,25 @@
 
 #define _GNU_SOURCE
 
+#include <elf.h>
 #include <pthread.h>
 #include <stdbool.h>
 
+#include <sys/ptrace.h>
+#include <sys/uio.h>
+#include <sys/wait.h>
+
 #include "helpers.h"
 #include "xstate.h"
 
+static inline uint64_t xgetbv(uint32_t index)
+{
+	uint32_t eax, edx;
+
+	asm volatile("xgetbv" : "=a" (eax), "=d" (edx) : "c" (index));
+	return eax + ((uint64_t)edx << 32);
+}
+
 static struct xstate_info xstate;
 
 struct futex_info {
@@ -27,6 +40,19 @@ static inline void load_rand_xstate(struct xstate_info *xstate, struct xsave_buf
 	xrstor(xbuf, xstate->mask);
 }
 
+static inline void load_init_xstate(struct xstate_info *xstate, struct xsave_buffer *xbuf)
+{
+	clear_xstate_header(xbuf);
+	xrstor(xbuf, xstate->mask);
+}
+
+static inline void copy_xstate(struct xsave_buffer *xbuf_dst, struct xsave_buffer *xbuf_src)
+{
+	memcpy(&xbuf_dst->bytes[xstate.xbuf_offset],
+	       &xbuf_src->bytes[xstate.xbuf_offset],
+	       xstate.size);
+}
+
 static inline bool validate_xstate_same(struct xsave_buffer *xbuf1, struct xsave_buffer *xbuf2)
 {
 	int ret;
@@ -196,3 +222,106 @@ void test_context_switch(uint32_t feature_num, uint32_t num_threads, uint32_t it
 
 	free(finfo);
 }
+
+/*
+ * Ptrace test for the ABI format as described in arch/x86/include/asm/user.h
+ */
+
+/*
+ * Make sure the ptracee has the expanded kernel buffer on the first use.
+ * Then, initialize the state before performing the state injection from
+ * the ptracer. For non-dynamic states, this is benign.
+ */
+static inline void ptracee_touch_xstate(void)
+{
+	struct xsave_buffer *xbuf;
+
+	xbuf = alloc_xbuf();
+
+	load_rand_xstate(&xstate, xbuf);
+	load_init_xstate(&xstate, xbuf);
+
+	free(xbuf);
+}
+
+/*
+ * Ptracer injects the randomized xstate data. It also reads before and
+ * after that, which will execute the kernel's state copy functions.
+ */
+static void ptracer_inject_xstate(pid_t target)
+{
+	uint32_t xbuf_size = get_xbuf_size();
+	struct xsave_buffer *xbuf1, *xbuf2;
+	struct iovec iov;
+
+	/*
+	 * Allocate buffers to keep data while ptracer can write the
+	 * other buffer
+	 */
+	xbuf1 = alloc_xbuf();
+	xbuf2 = alloc_xbuf();
+	if (!xbuf1 || !xbuf2)
+		ksft_exit_fail_msg("unable to allocate XSAVE buffer\n");
+
+	iov.iov_base = xbuf1;
+	iov.iov_len  = xbuf_size;
+
+	if (ptrace(PTRACE_GETREGSET, target, (uint32_t)NT_X86_XSTATE, &iov))
+		ksft_exit_fail_msg("PTRACE_GETREGSET failed\n");
+
+	printf("[RUN]\t%s: inject xstate via ptrace().\n", xstate.name);
+
+	load_rand_xstate(&xstate, xbuf1);
+	copy_xstate(xbuf2, xbuf1);
+
+	if (ptrace(PTRACE_SETREGSET, target, (uint32_t)NT_X86_XSTATE, &iov))
+		ksft_exit_fail_msg("PTRACE_SETREGSET failed\n");
+
+	if (ptrace(PTRACE_GETREGSET, target, (uint32_t)NT_X86_XSTATE, &iov))
+		ksft_exit_fail_msg("PTRACE_GETREGSET failed\n");
+
+	if (*(uint64_t *)get_fpx_sw_bytes(xbuf1) == xgetbv(0))
+		printf("[OK]\t'xfeatures' in SW reserved area was correctly written\n");
+	else
+		printf("[FAIL]\t'xfeatures' in SW reserved area was not correctly written\n");
+
+	if (validate_xstate_same(xbuf2, xbuf1))
+		printf("[OK]\txstate was correctly updated.\n");
+	else
+		printf("[FAIL]\txstate was not correctly updated.\n");
+
+	free(xbuf1);
+	free(xbuf2);
+}
+
+void test_ptrace(uint32_t feature_num)
+{
+	pid_t child;
+	int status;
+
+	xstate = get_xstate_info(feature_num);
+
+	child = fork();
+	if (child < 0) {
+		ksft_exit_fail_msg("fork() failed\n");
+	} else if (!child) {
+		if (ptrace(PTRACE_TRACEME, 0, NULL, NULL))
+			ksft_exit_fail_msg("PTRACE_TRACEME failed\n");
+
+		ptracee_touch_xstate();
+
+		raise(SIGTRAP);
+		_exit(0);
+	}
+
+	do {
+		wait(&status);
+	} while (WSTOPSIG(status) != SIGTRAP);
+
+	ptracer_inject_xstate(child);
+
+	ptrace(PTRACE_DETACH, child, NULL, NULL);
+	wait(&status);
+	if (!WIFEXITED(status) || WEXITSTATUS(status))
+		ksft_exit_fail_msg("ptracee exit error\n");
+}

tools/testing/selftests/x86/xstate.h

@@ -190,5 +190,6 @@ static inline void set_rand_data(struct xstate_info *xstate, struct xsave_buffer
 }
 
 void test_context_switch(uint32_t feature_num, uint32_t num_threads, uint32_t iterations);
+void test_ptrace(uint32_t feature_num);
 
 #endif /* __SELFTESTS_X86_XSTATE_H */