If I do SYSCALL with EFLAGS.TF set from compat mode on Intel hardware
with -cpu host and no other funny business, the guest kernel seems to
get #DB with the stored IP pointing at the SYSCALL instruction. This
is wrong -- SYSCALL is #UD, which is a *fault*, so there shouldn't be
a single-step trap.
Unless I'm missing something in the code, emulate_ud() is mishandled
in general -- it seems to make cause inject_emulated_exception() to
return false here:
if (ctxt->have_exception) {
r = EMULATE_DONE;
if (inject_emulated_exception(vcpu))
return r;
and then we land here:
if (r == EMULATE_DONE && ctxt->tf)
kvm_vcpu_do_singlestep(vcpu, &r);
if TF was set, which is wrong.
You can test this by applying the attached patch, building x86
selftests, and running syscall_arg_fault_32 in a VM. It hangs. It
should complete successfully, and it does on bare metal.
commit fae8e860584b5a8c2253b522cb478e92b8b0c281
Author: Andy Lutomirski <luto@xxxxxxxxxx>
Date: Fri Jun 28 19:54:34 2019 -0700
selftests/x86: Test SYSCALL and SYSENTER manually with TF set
Make sure that we exercise both variants of the nasty
TF-in-compat-syscall regardless of what vendor's CPU is running the
tests.
Also change the intentional signal after SYSCALL to use ud2, which
is a lot more comprehensible.
This crashes the kernel due to an FSGSBASE bug right now.
Reported-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Cc: "Bae, Chang Seok" <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index 186520198de7..fa07d526fe39 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -12,8 +12,9 @@ CAN_BUILD_WITH_NOPIE := $(shell ./check_cc.sh $(CC) trivial_program.c -no-pie)
TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt test_mremap_vdso \
check_initial_reg_state sigreturn iopl mpx-mini-test ioperm \
- protection_keys test_vdso test_vsyscall mov_ss_trap
-TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault test_syscall_vdso unwind_vdso \
+ protection_keys test_vdso test_vsyscall mov_ss_trap \
+ syscall_arg_fault
+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
diff --git a/tools/testing/selftests/x86/syscall_arg_fault.c b/tools/testing/selftests/x86/syscall_arg_fault.c
index 4e25d38c8bbd..939de3c94976 100644
--- a/tools/testing/selftests/x86/syscall_arg_fault.c
+++ b/tools/testing/selftests/x86/syscall_arg_fault.c
@@ -15,9 +15,30 @@
#include <setjmp.h>
#include <errno.h>
+#ifdef __x86_64__
+# define WIDTH "q"
+#else
+# define WIDTH "l"
+#endif
+
/* Our sigaltstack scratch space. */
static unsigned char altstack_data[SIGSTKSZ];
+static unsigned long get_eflags(void)
+{
+ unsigned long eflags;
+ asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
+ return eflags;
+}
+
+static void set_eflags(unsigned long eflags)
+{
+ asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
+ : : "rm" (eflags) : "flags");
+}
+
+#define X86_EFLAGS_TF (1UL << 8)
+
static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
int flags)
{
@@ -35,13 +56,22 @@ static sigjmp_buf jmpbuf;
static volatile sig_atomic_t n_errs;
+#ifdef __x86_64__
+#define REG_AX REG_RAX
+#define REG_IP REG_RIP
+#else
+#define REG_AX REG_EAX
+#define REG_IP REG_EIP
+#endif
+
static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void)
{
ucontext_t *ctx = (ucontext_t*)ctx_void;
+ long ax = (long)ctx->uc_mcontext.gregs[REG_AX];
- if (ctx->uc_mcontext.gregs[REG_EAX] != -EFAULT) {
- printf("[FAIL]\tAX had the wrong value: 0x%x\n",
- ctx->uc_mcontext.gregs[REG_EAX]);
+ if (ax != -EFAULT && ax != -ENOSYS) {
+ printf("[FAIL]\tAX had the wrong value: 0x%lx\n",
+ (unsigned long)ax);
n_errs++;
} else {
printf("[OK]\tSeems okay\n");
@@ -50,9 +80,21 @@ static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void)
siglongjmp(jmpbuf, 1);
}
+static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
+{
+}
+
static void sigill(int sig, siginfo_t *info, void *ctx_void)
{
- printf("[SKIP]\tIllegal instruction\n");
+ ucontext_t *ctx = (ucontext_t*)ctx_void;
+ unsigned short *ip = (unsigned short *)ctx->uc_mcontext.gregs[REG_IP];
+
+ if (*ip == 0x0b0f) {
+ /* one of the ud2 instructions faulted */
+ printf("[OK]\tSYSCALL returned normally\n");
+ } else {
+ printf("[SKIP]\tIllegal instruction\n");
+ }
siglongjmp(jmpbuf, 1);
}
@@ -120,9 +162,46 @@ int main()
"movl $-1, %%ebp\n\t"
"movl $-1, %%esp\n\t"
"syscall\n\t"
- "pushl $0" /* make sure we segfault cleanly */
+ "ud2" /* make sure we recover cleanly */
+ : : : "memory", "flags");
+ }
+
+ printf("[RUN]\tSYSENTER with TF and invalid state\n");
+ sethandler(SIGTRAP, sigtrap, SA_ONSTACK);
+
+ if (sigsetjmp(jmpbuf, 1) == 0) {
+ set_eflags(get_eflags() | X86_EFLAGS_TF);
+ asm volatile (
+ "movl $-1, %%eax\n\t"
+ "movl $-1, %%ebx\n\t"
+ "movl $-1, %%ecx\n\t"
+ "movl $-1, %%edx\n\t"
+ "movl $-1, %%esi\n\t"
+ "movl $-1, %%edi\n\t"
+ "movl $-1, %%ebp\n\t"
+ "movl $-1, %%esp\n\t"
+ "sysenter"
+ : : : "memory", "flags");
+ }
+ set_eflags(get_eflags() & ~X86_EFLAGS_TF);
+
+ printf("[RUN]\tSYSCALL with TF and invalid state\n");
+ if (sigsetjmp(jmpbuf, 1) == 0) {
+ set_eflags(get_eflags() | X86_EFLAGS_TF);
+ asm volatile (
+ "movl $-1, %%eax\n\t"
+ "movl $-1, %%ebx\n\t"
+ "movl $-1, %%ecx\n\t"
+ "movl $-1, %%edx\n\t"
+ "movl $-1, %%esi\n\t"
+ "movl $-1, %%edi\n\t"
+ "movl $-1, %%ebp\n\t"
+ "movl $-1, %%esp\n\t"
+ "syscall\n\t"
+ "ud2" /* make sure we recover cleanly */
: : : "memory", "flags");
}
+ set_eflags(get_eflags() & ~X86_EFLAGS_TF);
return 0;
}
