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selftests/x86/amx: Add test cases for AMX state management 

AMX TILEDATA is a very large XSAVE feature.  It could have caused
nasty XSAVE buffer space waste in two places:

 * Signal stacks
 * Kernel task_struct->fpu buffers

To avoid this waste, neither of these buffers have AMX state by
default.  The non-default features are called "dynamic" features.

There is an arch_prctl(ARCH_REQ_XCOMP_PERM) which allows a task
to declare that it wants to use AMX or other "dynamic" XSAVE
features.  This arch_prctl() ensures that sufficient sigaltstack
space is available before it will succeed.  It also expands the
task_struct buffer.

Functions of this test:
 * Test arch_prctl(ARCH_REQ_XCOMP_PERM).  Ensure that it checks for
   proper sigaltstack sizing and that the sizing is enforced for
   future sigaltstack calls.
 * Ensure that ARCH_REQ_XCOMP_PERM is inherited across fork()
 * Ensure that TILEDATA use before the prctl() is fatal
 * Ensure that TILEDATA is cleared across fork()

Note: Generally, compiler support is needed to do something with
AMX.  Instead, directly load AMX state from userspace with a
plain XSAVE.  Do not depend on the compiler.

 [ dhansen: bunches of cleanups ]

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211026122524.7BEDAA95@davehans-spike.ostc.intel.com
This commit is contained in:
Chang S. Bae 2021-10-26 05:25:24 -07:00 committed by Borislav Petkov
parent 2308ee57d9
commit 6a3e0651b4
2 changed files with 698 additions and 1 deletions
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2
tools/testing/selftests/x86/Makefile
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@ -18,7 +18,7 @@ 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
corrupt_xstate_header amx
# Some selftests require 32bit support enabled also on 64bit systems
TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall

697
tools/testing/selftests/x86/amx.c Normal file
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@ -0,0 +1,697 @@
// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE
#include <err.h>
#include <errno.h>
#include <setjmp.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include <unistd.h>
#include <x86intrin.h>
#include <linux/futex.h>
#include <sys/auxv.h>
#include <sys/mman.h>
#include <sys/shm.h>
#include <sys/syscall.h>
#include <sys/wait.h>
#ifndef __x86_64__
# error This test is 64-bit only
#endif
#define XSAVE_HDR_OFFSET 512
#define XSAVE_HDR_SIZE 64
struct xsave_buffer {
union {
struct {
char legacy[XSAVE_HDR_OFFSET];
char header[XSAVE_HDR_SIZE];
char extended[0];
};
char bytes[0];
};
};
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 inline void cpuid(uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx)
{
asm volatile("cpuid;"
: "=a" (*eax), "=b" (*ebx), "=c" (*ecx), "=d" (*edx)
: "0" (*eax), "2" (*ecx));
}
static inline void xsave(struct xsave_buffer *xbuf, uint64_t rfbm)
{
uint32_t rfbm_lo = rfbm;
uint32_t rfbm_hi = rfbm >> 32;
asm volatile("xsave (%%rdi)"
: : "D" (xbuf), "a" (rfbm_lo), "d" (rfbm_hi)
: "memory");
}
static inline void xrstor(struct xsave_buffer *xbuf, uint64_t rfbm)
{
uint32_t rfbm_lo = rfbm;
uint32_t rfbm_hi = rfbm >> 32;
asm volatile("xrstor (%%rdi)"
: : "D" (xbuf), "a" (rfbm_lo), "d" (rfbm_hi));
}
/* err() exits and will not return */
#define fatal_error(msg, ...) err(1, "[FAIL]\t" msg, ##__VA_ARGS__)
static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
int flags)
{
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_sigaction = handler;
sa.sa_flags = SA_SIGINFO | flags;
sigemptyset(&sa.sa_mask);
if (sigaction(sig, &sa, 0))
fatal_error("sigaction");
}
static void clearhandler(int sig)
{
struct sigaction sa;
memset(&sa, 0, sizeof(sa));
sa.sa_handler = SIG_DFL;
sigemptyset(&sa.sa_mask);
if (sigaction(sig, &sa, 0))
fatal_error("sigaction");
}
#define XFEATURE_XTILECFG 17
#define XFEATURE_XTILEDATA 18
#define XFEATURE_MASK_XTILECFG (1 << XFEATURE_XTILECFG)
#define XFEATURE_MASK_XTILEDATA (1 << XFEATURE_XTILEDATA)
#define XFEATURE_MASK_XTILE (XFEATURE_MASK_XTILECFG | XFEATURE_MASK_XTILEDATA)
#define CPUID_LEAF1_ECX_XSAVE_MASK (1 << 26)
#define CPUID_LEAF1_ECX_OSXSAVE_MASK (1 << 27)
static inline void check_cpuid_xsave(void)
{
uint32_t eax, ebx, ecx, edx;
/*
* CPUID.1:ECX.XSAVE[bit 26] enumerates general
* support for the XSAVE feature set, including
* XGETBV.
*/
eax = 1;
ecx = 0;
cpuid(&eax, &ebx, &ecx, &edx);
if (!(ecx & CPUID_LEAF1_ECX_XSAVE_MASK))
fatal_error("cpuid: no CPU xsave support");
if (!(ecx & CPUID_LEAF1_ECX_OSXSAVE_MASK))
fatal_error("cpuid: no OS xsave support");
}
static uint32_t xbuf_size;
static struct {
uint32_t xbuf_offset;
uint32_t size;
} xtiledata;
#define CPUID_LEAF_XSTATE 0xd
#define CPUID_SUBLEAF_XSTATE_USER 0x0
#define TILE_CPUID 0x1d
#define TILE_PALETTE_ID 0x1
static void check_cpuid_xtiledata(void)
{
uint32_t eax, ebx, ecx, edx;
eax = CPUID_LEAF_XSTATE;
ecx = CPUID_SUBLEAF_XSTATE_USER;
cpuid(&eax, &ebx, &ecx, &edx);
/*
* EBX enumerates the size (in bytes) required by the XSAVE
* instruction for an XSAVE area containing all the user state
* components corresponding to bits currently set in XCR0.
*
* Stash that off so it can be used to allocate buffers later.
*/
xbuf_size = ebx;
eax = CPUID_LEAF_XSTATE;
ecx = XFEATURE_XTILEDATA;
cpuid(&eax, &ebx, &ecx, &edx);
/*
* eax: XTILEDATA state component size
* ebx: XTILEDATA state component offset in user buffer
*/
if (!eax || !ebx)
fatal_error("xstate cpuid: invalid tile data size/offset: %d/%d",
eax, ebx);
xtiledata.size = eax;
xtiledata.xbuf_offset = ebx;
}
/* The helpers for managing XSAVE buffer and tile states: */
struct xsave_buffer *alloc_xbuf(void)
{
struct xsave_buffer *xbuf;
/* XSAVE buffer should be 64B-aligned. */
xbuf = aligned_alloc(64, xbuf_size);
if (!xbuf)
fatal_error("aligned_alloc()");
return xbuf;
}
static inline void clear_xstate_header(struct xsave_buffer *buffer)
{
memset(&buffer->header, 0, sizeof(buffer->header));
}
static inline uint64_t get_xstatebv(struct xsave_buffer *buffer)
{
/* XSTATE_BV is at the beginning of the header: */
return *(uint64_t *)&buffer->header;
}
static inline void set_xstatebv(struct xsave_buffer *buffer, uint64_t bv)
{
/* XSTATE_BV is at the beginning of the header: */
*(uint64_t *)(&buffer->header) = bv;
}
static void set_rand_tiledata(struct xsave_buffer *xbuf)
{
int *ptr = (int *)&xbuf->bytes[xtiledata.xbuf_offset];
int data;
int i;
/*
* Ensure that 'data' is never 0. This ensures that
* the registers are never in their initial configuration
* and thus never tracked as being in the init state.
*/
data = rand() | 1;
for (i = 0; i < xtiledata.size / sizeof(int); i++, ptr++)
*ptr = data;
}
struct xsave_buffer *stashed_xsave;
static void init_stashed_xsave(void)
{
stashed_xsave = alloc_xbuf();
if (!stashed_xsave)
fatal_error("failed to allocate stashed_xsave\n");
clear_xstate_header(stashed_xsave);
}
static void free_stashed_xsave(void)
{
free(stashed_xsave);
}
/* 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. */
#define SW_BYTES_BV_OFFSET (SW_BYTES_OFFSET + 8)
static inline struct _fpx_sw_bytes *get_fpx_sw_bytes(void *buffer)
{
return (struct _fpx_sw_bytes *)(buffer + SW_BYTES_OFFSET);
}
static inline uint64_t get_fpx_sw_bytes_features(void *buffer)
{
return *(uint64_t *)(buffer + SW_BYTES_BV_OFFSET);
}
/* Work around printf() being unsafe in signals: */
#define SIGNAL_BUF_LEN 1000
char signal_message_buffer[SIGNAL_BUF_LEN];
void sig_print(char *msg)
{
int left = SIGNAL_BUF_LEN - strlen(signal_message_buffer) - 1;
strncat(signal_message_buffer, msg, left);
}
static volatile bool noperm_signaled;
static int noperm_errs;
/*
* Signal handler for when AMX is used but
* permission has not been obtained.
*/
static void handle_noperm(int sig, siginfo_t *si, void *ctx_void)
{
ucontext_t *ctx = (ucontext_t *)ctx_void;
void *xbuf = ctx->uc_mcontext.fpregs;
struct _fpx_sw_bytes *sw_bytes;
uint64_t features;
/* Reset the signal message buffer: */
signal_message_buffer[0] = '\0';
sig_print("\tAt SIGILL handler,\n");
if (si->si_code != ILL_ILLOPC) {
noperm_errs++;
sig_print("[FAIL]\tInvalid signal code.\n");
} else {
sig_print("[OK]\tValid signal code (ILL_ILLOPC).\n");
}
sw_bytes = get_fpx_sw_bytes(xbuf);
/*
* Without permission, the signal XSAVE buffer should not
* have room for AMX register state (aka. xtiledata).
* Check that the size does not overlap with where xtiledata
* will reside.
*
* This also implies that no state components *PAST*
* XTILEDATA (features >=19) can be present in the buffer.
*/
if (sw_bytes->xstate_size <= xtiledata.xbuf_offset) {
sig_print("[OK]\tValid xstate size\n");
} else {
noperm_errs++;
sig_print("[FAIL]\tInvalid xstate size\n");
}
features = get_fpx_sw_bytes_features(xbuf);
/*
* Without permission, the XTILEDATA feature
* bit should not be set.
*/
if ((features & XFEATURE_MASK_XTILEDATA) == 0) {
sig_print("[OK]\tValid xstate mask\n");
} else {
noperm_errs++;
sig_print("[FAIL]\tInvalid xstate mask\n");
}
noperm_signaled = true;
ctx->uc_mcontext.gregs[REG_RIP] += 3; /* Skip the faulting XRSTOR */
}
/* Return true if XRSTOR is successful; otherwise, false. */
static inline bool xrstor_safe(struct xsave_buffer *xbuf, uint64_t mask)
{
noperm_signaled = false;
xrstor(xbuf, mask);
/* Print any messages produced by the signal code: */
printf("%s", signal_message_buffer);
/*
* Reset the buffer to make sure any future printing
* only outputs new messages:
*/
signal_message_buffer[0] = '\0';
if (noperm_errs)
fatal_error("saw %d errors in noperm signal handler\n", noperm_errs);
return !noperm_signaled;
}
/*
* Use XRSTOR to populate the XTILEDATA registers with
* random data.
*
* Return true if successful; otherwise, false.
*/
static inline bool load_rand_tiledata(struct xsave_buffer *xbuf)
{
clear_xstate_header(xbuf);
set_xstatebv(xbuf, XFEATURE_MASK_XTILEDATA);
set_rand_tiledata(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 */
#define ARCH_GET_XCOMP_PERM 0x1022
#define ARCH_REQ_XCOMP_PERM 0x1023
static void req_xtiledata_perm(void)
{
syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_PERM, XFEATURE_XTILEDATA);
}
static void validate_req_xcomp_perm(enum expected_result exp)
{
unsigned long bitmask;
long rc;
rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_PERM, XFEATURE_XTILEDATA);
if (exp == FAIL_EXPECTED) {
if (rc) {
printf("[OK]\tARCH_REQ_XCOMP_PERM saw expected failure..\n");
return;
}
fatal_error("ARCH_REQ_XCOMP_PERM saw unexpected success.\n");
} else if (rc) {
fatal_error("ARCH_REQ_XCOMP_PERM saw unexpected failure.\n");
}
rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_PERM, &bitmask);
if (rc) {
fatal_error("prctl(ARCH_GET_XCOMP_PERM) error: %ld", rc);
} else if (bitmask & XFEATURE_MASK_XTILE) {
printf("\tARCH_REQ_XCOMP_PERM is successful.\n");
}
}
static void validate_xcomp_perm(enum expected_result exp)
{
bool load_success = load_rand_tiledata(stashed_xsave);
if (exp == FAIL_EXPECTED) {
if (load_success) {
noperm_errs++;
printf("[FAIL]\tLoad tiledata succeeded.\n");
} else {
printf("[OK]\tLoad tiledata failed.\n");
}
} else if (exp == SUCCESS_EXPECTED) {
if (load_success) {
printf("[OK]\tLoad tiledata succeeded.\n");
} else {
noperm_errs++;
printf("[FAIL]\tLoad tiledata failed.\n");
}
}
}
#ifndef AT_MINSIGSTKSZ
# define AT_MINSIGSTKSZ 51
#endif
static void *alloc_altstack(unsigned int size)
{
void *altstack;
altstack = mmap(NULL, size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
if (altstack == MAP_FAILED)
fatal_error("mmap() for altstack");
return altstack;
}
static void setup_altstack(void *addr, unsigned long size, enum expected_result exp)
{
stack_t ss;
int rc;
memset(&ss, 0, sizeof(ss));
ss.ss_size = size;
ss.ss_sp = addr;
rc = sigaltstack(&ss, NULL);
if (exp == FAIL_EXPECTED) {
if (rc) {
printf("[OK]\tsigaltstack() failed.\n");
} else {
fatal_error("sigaltstack() succeeded unexpectedly.\n");
}
} else if (rc) {
fatal_error("sigaltstack()");
}
}
static void test_dynamic_sigaltstack(void)
{
unsigned int small_size, enough_size;
unsigned long minsigstksz;
void *altstack;
minsigstksz = getauxval(AT_MINSIGSTKSZ);
printf("\tAT_MINSIGSTKSZ = %lu\n", minsigstksz);
/*
* getauxval() itself can return 0 for failure or
* success. But, in this case, AT_MINSIGSTKSZ
* will always return a >=0 value if implemented.
* Just check for 0.
*/
if (minsigstksz == 0) {
printf("no support for AT_MINSIGSTKSZ, skipping sigaltstack tests\n");
return;
}
enough_size = minsigstksz * 2;
altstack = alloc_altstack(enough_size);
printf("\tAllocate memory for altstack (%u bytes).\n", enough_size);
/*
* Try setup_altstack() with a size which can not fit
* XTILEDATA. ARCH_REQ_XCOMP_PERM should fail.
*/
small_size = minsigstksz - xtiledata.size;
printf("\tAfter sigaltstack() with small size (%u bytes).\n", small_size);
setup_altstack(altstack, small_size, SUCCESS_EXPECTED);
validate_req_xcomp_perm(FAIL_EXPECTED);
/*
* Try setup_altstack() with a size derived from
* AT_MINSIGSTKSZ. It should be more than large enough
* and thus ARCH_REQ_XCOMP_PERM should succeed.
*/
printf("\tAfter sigaltstack() with enough size (%u bytes).\n", enough_size);
setup_altstack(altstack, enough_size, SUCCESS_EXPECTED);
validate_req_xcomp_perm(SUCCESS_EXPECTED);
/*
* Try to coerce setup_altstack() to again accept a
* too-small altstack. This ensures that big-enough
* sigaltstacks can not shrink to a too-small value
* once XTILEDATA permission is established.
*/
printf("\tThen, sigaltstack() with small size (%u bytes).\n", small_size);
setup_altstack(altstack, small_size, FAIL_EXPECTED);
}
static void test_dynamic_state(void)
{
pid_t parent, child, grandchild;
parent = fork();
if (parent < 0) {
/* fork() failed */
fatal_error("fork");
} else if (parent > 0) {
int status;
/* fork() succeeded. Now in the parent. */
wait(&status);
if (!WIFEXITED(status) || WEXITSTATUS(status))
fatal_error("arch_prctl test parent exit");
return;
}
/* fork() succeeded. Now in the child . */
printf("[RUN]\tCheck ARCH_REQ_XCOMP_PERM around process fork() and sigaltack() test.\n");
printf("\tFork a child.\n");
child = fork();
if (child < 0) {
fatal_error("fork");
} else if (child > 0) {
int status;
wait(&status);
if (!WIFEXITED(status) || WEXITSTATUS(status))
fatal_error("arch_prctl test child exit");
_exit(0);
}
/*
* The permission request should fail without an
* XTILEDATA-compatible signal stack
*/
printf("\tTest XCOMP_PERM at child.\n");
validate_xcomp_perm(FAIL_EXPECTED);
/*
* Set up an XTILEDATA-compatible signal stack and
* also obtain permission to populate XTILEDATA.
*/
printf("\tTest dynamic sigaltstack at child:\n");
test_dynamic_sigaltstack();
/* Ensure that XTILEDATA can be populated. */
printf("\tTest XCOMP_PERM again at child.\n");
validate_xcomp_perm(SUCCESS_EXPECTED);
printf("\tFork a grandchild.\n");
grandchild = fork();
if (grandchild < 0) {
/* fork() failed */
fatal_error("fork");
} else if (!grandchild) {
/* fork() succeeded. Now in the (grand)child. */
printf("\tTest XCOMP_PERM at grandchild.\n");
/*
* Ensure that the grandchild inherited
* permission and a compatible sigaltstack:
*/
validate_xcomp_perm(SUCCESS_EXPECTED);
} else {
int status;
/* fork() succeeded. Now in the parent. */
wait(&status);
if (!WIFEXITED(status) || WEXITSTATUS(status))
fatal_error("fork test grandchild");
}
_exit(0);
}
/*
* Save current register state and compare it to @xbuf1.'
*
* Returns false if @xbuf1 matches the registers.
* Returns true if @xbuf1 differs from the registers.
*/
static inline bool __validate_tiledata_regs(struct xsave_buffer *xbuf1)
{
struct xsave_buffer *xbuf2;
int ret;
xbuf2 = alloc_xbuf();
if (!xbuf2)
fatal_error("failed to allocate XSAVE buffer\n");
xsave(xbuf2, XFEATURE_MASK_XTILEDATA);
ret = memcmp(&xbuf1->bytes[xtiledata.xbuf_offset],
&xbuf2->bytes[xtiledata.xbuf_offset],
xtiledata.size);
free(xbuf2);
if (ret == 0)
return false;
return true;
}
static inline void validate_tiledata_regs_same(struct xsave_buffer *xbuf)
{
int ret = __validate_tiledata_regs(xbuf);
if (ret != 0)
fatal_error("TILEDATA registers changed");
}
static inline void validate_tiledata_regs_changed(struct xsave_buffer *xbuf)
{
int ret = __validate_tiledata_regs(xbuf);
if (ret == 0)
fatal_error("TILEDATA registers did not change");
}
/* tiledata inheritance test */
static void test_fork(void)
{
pid_t child, grandchild;
child = fork();
if (child < 0) {
/* fork() failed */
fatal_error("fork");
} else if (child > 0) {
/* fork() succeeded. Now in the parent. */
int status;
wait(&status);
if (!WIFEXITED(status) || WEXITSTATUS(status))
fatal_error("fork test child");
return;
}
/* fork() succeeded. Now in the child. */
printf("[RUN]\tCheck tile data inheritance.\n\tBefore fork(), load tiledata\n");
load_rand_tiledata(stashed_xsave);
grandchild = fork();
if (grandchild < 0) {
/* fork() failed */
fatal_error("fork");
} else if (grandchild > 0) {
/* fork() succeeded. Still in the first child. */
int status;
wait(&status);
if (!WIFEXITED(status) || WEXITSTATUS(status))
fatal_error("fork test grand child");
_exit(0);
}
/* fork() succeeded. Now in the (grand)child. */
/*
* TILEDATA registers are not preserved across fork().
* Ensure that their value has changed:
*/
validate_tiledata_regs_changed(stashed_xsave);
_exit(0);
}
int main(void)
{
/* Check hardware availability at first */
check_cpuid_xsave();
check_cpuid_xtiledata();
init_stashed_xsave();
sethandler(SIGILL, handle_noperm, 0);
test_dynamic_state();
/* Request permission for the following tests */
req_xtiledata_perm();
test_fork();
clearhandler(SIGILL);
free_stashed_xsave();
return 0;
}