From: Andy Lutomirski <[email protected]>
This is very heavily based on some code from Thomas Gleixner. On a system
without XSAVES, it triggers the WARN_ON():
Bad FPU state detected at copy_kernel_to_fpregs+0x2f/0x40, reinitializing FPU registers.
Signed-off-by: Andy Lutomirski <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
---
V2: main() -> main(void) - Borislav
---
tools/testing/selftests/x86/Makefile | 3
tools/testing/selftests/x86/corrupt_xstate_header.c | 114 ++++++++++++++++++++
2 files changed, 116 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/x86/corrupt_xstate_header.c
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -17,7 +17,8 @@ TARGETS_C_BOTHBITS := single_step_syscal
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
+TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
+ corrupt_xstate_header
# Some selftests require 32bit support enabled also on 64bit systems
TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall
--- /dev/null
+++ b/tools/testing/selftests/x86/corrupt_xstate_header.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Corrupt the XSTATE header in a signal frame
+ *
+ * Based on analysis and a test case from Thomas Gleixner.
+ */
+
+#define _GNU_SOURCE
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <sched.h>
+#include <signal.h>
+#include <err.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <sys/wait.h>
+
+static inline void __cpuid(unsigned int *eax, unsigned int *ebx,
+ unsigned int *ecx, unsigned int *edx)
+{
+ asm volatile(
+ "cpuid;"
+ : "=a" (*eax),
+ "=b" (*ebx),
+ "=c" (*ecx),
+ "=d" (*edx)
+ : "0" (*eax), "2" (*ecx));
+}
+
+static inline int xsave_enabled(void)
+{
+ unsigned int eax, ebx, ecx, edx;
+
+ eax = 0x1;
+ ecx = 0x0;
+ __cpuid(&eax, &ebx, &ecx, &edx);
+
+ /* Is CR4.OSXSAVE enabled ? */
+ return ecx & (1U << 27);
+}
+
+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))
+ err(1, "sigaction");
+}
+
+static void sigusr1(int sig, siginfo_t *info, void *uc_void)
+{
+ ucontext_t *uc = uc_void;
+ uint8_t *fpstate = (uint8_t *)uc->uc_mcontext.fpregs;
+ uint64_t *xfeatures = (uint64_t *)(fpstate + 512);
+
+ printf("\tWreckage XSTATE header\n");
+ /* Wreckage the first reserved byte in the header */
+ *(xfeatures + 2) = 0xfffffff;
+}
+
+static void sigsegv(int sig, siginfo_t *info, void *uc_void)
+{
+ printf("\tGot SIGSEGV\n");
+}
+
+int main(void)
+{
+ cpu_set_t set;
+
+ sethandler(SIGUSR1, sigusr1, 0);
+ sethandler(SIGSEGV, sigsegv, 0);
+
+ if (!xsave_enabled()) {
+ printf("[SKIP] CR4.OSXSAVE disabled.\n");
+ return 0;
+ }
+
+ CPU_ZERO(&set);
+ CPU_SET(0, &set);
+
+ /*
+ * Enforce that the child runs on the same CPU
+ * which in turn forces a schedule.
+ */
+ sched_setaffinity(getpid(), sizeof(set), &set);
+
+ printf("[RUN]\tSend ourselves a signal\n");
+ raise(SIGUSR1);
+
+ printf("[OK]\tBack from the signal. Now schedule.\n");
+ pid_t child = fork();
+ if (child < 0)
+ err(1, "fork");
+ if (child == 0)
+ return 0;
+ if (child)
+ waitpid(child, NULL, 0);
+ printf("[OK]\tBack in the main thread.\n");
+
+ /*
+ * We could try to confirm that extended state is still preserved
+ * when we schedule. For now, the only indication of failure is
+ * a warning in the kernel logs.
+ */
+
+ return 0;
+}
On Tuesday, 2021-06-08 at 16:36:23 +02, Thomas Gleixner wrote:
> From: Andy Lutomirski <[email protected]>
>
> This is very heavily based on some code from Thomas Gleixner. On a system
> without XSAVES, it triggers the WARN_ON():
>
> Bad FPU state detected at copy_kernel_to_fpregs+0x2f/0x40, reinitializing FPU registers.
>
> Signed-off-by: Andy Lutomirski <[email protected]>
> Signed-off-by: Thomas Gleixner <[email protected]>
> ---
> V2: main() -> main(void) - Borislav
> ---
> tools/testing/selftests/x86/Makefile | 3
> tools/testing/selftests/x86/corrupt_xstate_header.c | 114 ++++++++++++++++++++
> 2 files changed, 116 insertions(+), 1 deletion(-)
> create mode 100644 tools/testing/selftests/x86/corrupt_xstate_header.c
>
> --- a/tools/testing/selftests/x86/Makefile
> +++ b/tools/testing/selftests/x86/Makefile
> @@ -17,7 +17,8 @@ TARGETS_C_BOTHBITS := single_step_syscal
> 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
> +TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
> + corrupt_xstate_header
> # Some selftests require 32bit support enabled also on 64bit systems
> TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall
>
> --- /dev/null
> +++ b/tools/testing/selftests/x86/corrupt_xstate_header.c
> @@ -0,0 +1,114 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Corrupt the XSTATE header in a signal frame
> + *
> + * Based on analysis and a test case from Thomas Gleixner.
> + */
> +
> +#define _GNU_SOURCE
> +
> +#include <stdlib.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <sched.h>
> +#include <signal.h>
> +#include <err.h>
> +#include <unistd.h>
> +#include <stdint.h>
> +#include <sys/wait.h>
> +
> +static inline void __cpuid(unsigned int *eax, unsigned int *ebx,
> + unsigned int *ecx, unsigned int *edx)
> +{
> + asm volatile(
> + "cpuid;"
> + : "=a" (*eax),
> + "=b" (*ebx),
> + "=c" (*ecx),
> + "=d" (*edx)
> + : "0" (*eax), "2" (*ecx));
> +}
> +
> +static inline int xsave_enabled(void)
> +{
> + unsigned int eax, ebx, ecx, edx;
> +
> + eax = 0x1;
> + ecx = 0x0;
> + __cpuid(&eax, &ebx, &ecx, &edx);
> +
> + /* Is CR4.OSXSAVE enabled ? */
> + return ecx & (1U << 27);
> +}
> +
> +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))
> + err(1, "sigaction");
> +}
> +
> +static void sigusr1(int sig, siginfo_t *info, void *uc_void)
> +{
> + ucontext_t *uc = uc_void;
> + uint8_t *fpstate = (uint8_t *)uc->uc_mcontext.fpregs;
> + uint64_t *xfeatures = (uint64_t *)(fpstate + 512);
> +
> + printf("\tWreckage XSTATE header\n");
"Wreckage" is an odd word to use here, as it usually refers to the
objects that are the result of a wreck. Maybe "wreck" or (to match the
test name) "corrupt"?
> + /* Wreckage the first reserved byte in the header */
> + *(xfeatures + 2) = 0xfffffff;
This trashes more than a byte, which doesn't seem significant, but it
would be good to have the comment and code match.
> +}
> +
> +static void sigsegv(int sig, siginfo_t *info, void *uc_void)
> +{
> + printf("\tGot SIGSEGV\n");
> +}
> +
> +int main(void)
> +{
> + cpu_set_t set;
> +
> + sethandler(SIGUSR1, sigusr1, 0);
> + sethandler(SIGSEGV, sigsegv, 0);
> +
> + if (!xsave_enabled()) {
> + printf("[SKIP] CR4.OSXSAVE disabled.\n");
> + return 0;
> + }
> +
> + CPU_ZERO(&set);
> + CPU_SET(0, &set);
> +
> + /*
> + * Enforce that the child runs on the same CPU
> + * which in turn forces a schedule.
> + */
> + sched_setaffinity(getpid(), sizeof(set), &set);
> +
> + printf("[RUN]\tSend ourselves a signal\n");
> + raise(SIGUSR1);
> +
> + printf("[OK]\tBack from the signal. Now schedule.\n");
> + pid_t child = fork();
> + if (child < 0)
> + err(1, "fork");
> + if (child == 0)
> + return 0;
> + if (child)
> + waitpid(child, NULL, 0);
> + printf("[OK]\tBack in the main thread.\n");
> +
> + /*
> + * We could try to confirm that extended state is still preserved
> + * when we schedule. For now, the only indication of failure is
> + * a warning in the kernel logs.
> + */
> +
> + return 0;
> +}
dme.
--
It's alright, we told you what to dream.
The following commit has been merged into the x86/fpu branch of tip:
Commit-ID: b7c11876d24bdd7ae3feeaa771b8f903f6cf05eb
Gitweb: https://git.kernel.org/tip/b7c11876d24bdd7ae3feeaa771b8f903f6cf05eb
Author: Andy Lutomirski <[email protected]>
AuthorDate: Tue, 08 Jun 2021 16:36:23 +02:00
Committer: Borislav Petkov <[email protected]>
CommitterDate: Wed, 09 Jun 2021 14:46:30 +02:00
selftests/x86: Test signal frame XSTATE header corruption handling
This is very heavily based on some code from Thomas Gleixner. On a system
without XSAVES, it triggers the WARN_ON():
Bad FPU state detected at copy_kernel_to_fpregs+0x2f/0x40, reinitializing FPU registers.
[ bp: Massage in nitpicks. ]
Signed-off-by: Andy Lutomirski <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Acked-by: Dave Hansen <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
tools/testing/selftests/x86/Makefile | 3 +-
tools/testing/selftests/x86/corrupt_xstate_header.c | 114 +++++++++++-
2 files changed, 116 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/x86/corrupt_xstate_header.c
diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index 65bba2a..b4142cd 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -17,7 +17,8 @@ TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt test_mremap
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
+TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
+ corrupt_xstate_header
# Some selftests require 32bit support enabled also on 64bit systems
TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall
diff --git a/tools/testing/selftests/x86/corrupt_xstate_header.c b/tools/testing/selftests/x86/corrupt_xstate_header.c
new file mode 100644
index 0000000..ab8599c
--- /dev/null
+++ b/tools/testing/selftests/x86/corrupt_xstate_header.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Corrupt the XSTATE header in a signal frame
+ *
+ * Based on analysis and a test case from Thomas Gleixner.
+ */
+
+#define _GNU_SOURCE
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <sched.h>
+#include <signal.h>
+#include <err.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <sys/wait.h>
+
+static inline void __cpuid(unsigned int *eax, unsigned int *ebx,
+ unsigned int *ecx, unsigned int *edx)
+{
+ asm volatile(
+ "cpuid;"
+ : "=a" (*eax),
+ "=b" (*ebx),
+ "=c" (*ecx),
+ "=d" (*edx)
+ : "0" (*eax), "2" (*ecx));
+}
+
+static inline int xsave_enabled(void)
+{
+ unsigned int eax, ebx, ecx, edx;
+
+ eax = 0x1;
+ ecx = 0x0;
+ __cpuid(&eax, &ebx, &ecx, &edx);
+
+ /* Is CR4.OSXSAVE enabled ? */
+ return ecx & (1U << 27);
+}
+
+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))
+ err(1, "sigaction");
+}
+
+static void sigusr1(int sig, siginfo_t *info, void *uc_void)
+{
+ ucontext_t *uc = uc_void;
+ uint8_t *fpstate = (uint8_t *)uc->uc_mcontext.fpregs;
+ uint64_t *xfeatures = (uint64_t *)(fpstate + 512);
+
+ printf("\tWreck XSTATE header\n");
+ /* Wreck the first reserved bytes in the header */
+ *(xfeatures + 2) = 0xfffffff;
+}
+
+static void sigsegv(int sig, siginfo_t *info, void *uc_void)
+{
+ printf("\tGot SIGSEGV\n");
+}
+
+int main(void)
+{
+ cpu_set_t set;
+
+ sethandler(SIGUSR1, sigusr1, 0);
+ sethandler(SIGSEGV, sigsegv, 0);
+
+ if (!xsave_enabled()) {
+ printf("[SKIP] CR4.OSXSAVE disabled.\n");
+ return 0;
+ }
+
+ CPU_ZERO(&set);
+ CPU_SET(0, &set);
+
+ /*
+ * Enforce that the child runs on the same CPU
+ * which in turn forces a schedule.
+ */
+ sched_setaffinity(getpid(), sizeof(set), &set);
+
+ printf("[RUN]\tSend ourselves a signal\n");
+ raise(SIGUSR1);
+
+ printf("[OK]\tBack from the signal. Now schedule.\n");
+ pid_t child = fork();
+ if (child < 0)
+ err(1, "fork");
+ if (child == 0)
+ return 0;
+ if (child)
+ waitpid(child, NULL, 0);
+ printf("[OK]\tBack in the main thread.\n");
+
+ /*
+ * We could try to confirm that extended state is still preserved
+ * when we schedule. For now, the only indication of failure is
+ * a warning in the kernel logs.
+ */
+
+ return 0;
+}