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 <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Rik van Riel <riel@surriel.com>
Link: https://lkml.kernel.org/r/20210608144346.234764986@linutronix.de

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index 65bba2ae86eee5f15d74a60e46ea6c13c24077e5..b4142cd1c5c23b82f323a0be79f8648df1d7f5d1 100644 (file)
--- 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 (file)
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;
+}