The current selftest asserts %r11 == %rflags after the 'syscall' returns
to userspace. However, such an assertion doesn't apply to the Intel FRED
system because, in that system, the 'syscall' instruction does not set
%r11=%rflags and %rcx=%rip.
Handle the FRED system case. Now, test that:
A) 'syscall' in a FRED system preserves %rcx and %r11.
B) 'syscall' in a non-FRED system sets %rcx=%rip and %r11=%rflags.
Note for the '__raise()' helper:
Those tests must manipulate registers before the 'syscall' instruction
is invoked. However, the current 'raise()' function from libc cannot
accomplish it. Therefore, create a syscall wrapper in inline Assembly to
control them.
Fixes: 660602140103 ("selftests/x86: Add a selftest for SYSRET to noncanonical addresses")
Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-786b55054126@xxxxxxxxx
Reported-by: Xin Li <xin3.li@xxxxxxxxx>
Co-developed-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Signed-off-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Signed-off-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>
---
tools/testing/selftests/x86/sysret_rip.c | 122 +++++++++++++++++++++--
1 file changed, 115 insertions(+), 7 deletions(-)
diff --git a/tools/testing/selftests/x86/sysret_rip.c b/tools/testing/selftests/x86/sysret_rip.c
index 84d74be1d90207ab..300104900192d396 100644
--- a/tools/testing/selftests/x86/sysret_rip.c
+++ b/tools/testing/selftests/x86/sysret_rip.c
@@ -39,6 +39,112 @@ asm (
extern const char test_page[];
static void const *current_test_page_addr = test_page;
+/*
+ * Arbitrary values.
+ */
+static const unsigned long r11_sentinel = 0xfeedfacedeadbeef;
+static const unsigned long rcx_sentinel = 0x5ca1ab1e0b57ac1e;
+
+/*
+ * An arbitrary *valid* RFLAGS value.
+ */
+static const unsigned long rflags_sentinel = 0x200a93;
+
+enum regs_ok {
+ REGS_UNDEFINED = -1,
+ REGS_SAVED = 0, /* Registers properly preserved (Intel FRED). */
+ REGS_SYSRET = 1 /* Registers match syscall/sysret. */
+};
+
+/*
+ * @rbx should be set to the syscall return %rip.
+ */
+static void check_regs_result(unsigned long r11, unsigned long rcx,
+ unsigned long rbx)
+{
+ static enum regs_ok regs_ok_state = REGS_UNDEFINED;
+ enum regs_ok ret;
+
+ if (r11 == r11_sentinel && rcx == rcx_sentinel) {
+ ret = REGS_SAVED;
+ } else if (r11 == rflags_sentinel && rcx == rbx) {
+ ret = REGS_SYSRET;
+ } else {
+ printf("[FAIL] check_regs_result\n");
+ printf(" r11_sentinel = %#lx; %%r11 = %#lx;\n", r11_sentinel, r11);
+ printf(" rcx_sentinel = %#lx; %%rcx = %#lx;\n", rcx_sentinel, rcx);
+ printf(" rflags_sentinel = %#lx\n", rflags_sentinel);
+ exit(1);
+ }
+
+
+ /*
+ * Test that we don't get a mix of REGS_SAVED and REGS_SYSRET.
+ * It needs at least calling check_regs_result() twice to assert.
+ */
+ if (regs_ok_state == REGS_UNDEFINED) {
+ /*
+ * First time calling check_regs_result().
+ */
+ regs_ok_state = ret;
+ } else {
+ assert(regs_ok_state == ret);
+ }
+}
+
+/*
+ * There are two cases:
+ *
+ * A) 'syscall' in a FRED system preserves %rcx and %r11.
+ * B) 'syscall' in a non-FRED system sets %rcx=%rip and %r11=%rflags.
+ *
+ * When the do_syscall() function is called for the first time,
+ * check_regs_result() will memorize the behavior, either (A) or (B).
+ * Then, the next do_syscall() call will verify that the 'syscall'
+ * behavior is the same.
+ *
+ * This function needs to be called at least twice to assert.
+ */
+static long do_syscall(long nr_syscall, unsigned long arg1, unsigned long arg2,
+ unsigned long arg3, unsigned long arg4,
+ unsigned long arg5, unsigned long arg6)
+{
+ unsigned long rbx;
+ unsigned long rcx = rcx_sentinel;
+ register unsigned long r11 __asm__("%r11") = r11_sentinel;
+ register unsigned long r10 __asm__("%r10") = arg4;
+ register unsigned long r8 __asm__("%r8") = arg5;
+ register unsigned long r9 __asm__("%r9") = arg6;
+
+ __asm__ volatile (
+ "movq -8(%%rsp), %%r12\n\t" // Do not clobber the red zone.
+ "pushq %[rflags_sentinel]\n\t"
+ "popfq\n\t"
+ "movq %%r12, -8(%%rsp)\n\t"
+ "leaq 1f(%%rip), %[rbx]\n\t"
+ "syscall\n"
+ "1:"
+
+ : "+a" (nr_syscall),
+ "+r" (r11),
+ "+c" (rcx),
+ [rbx] "=b" (rbx)
+
+ : [rflags_sentinel] "g" (rflags_sentinel),
+ "D" (arg1), /* %rdi */
+ "S" (arg2), /* %rsi */
+ "d" (arg3), /* %rdx */
+ "r" (r10),
+ "r" (r8),
+ "r" (r9)
+
+ : "r12", "memory"
+ );
+
+ check_regs_result(r11, rcx, rbx);
+ return nr_syscall;
+}
+
static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
int flags)
{
@@ -88,24 +194,26 @@ static void sigusr1(int sig, siginfo_t *info, void *ctx_void)
memcpy(&initial_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
+ check_regs_result(ctx->uc_mcontext.gregs[REG_R11],
+ ctx->uc_mcontext.gregs[REG_RCX],
+ ctx->uc_mcontext.gregs[REG_RBX]);
+
/* Set IP and CX to match so that SYSRET can happen. */
ctx->uc_mcontext.gregs[REG_RIP] = rip;
ctx->uc_mcontext.gregs[REG_RCX] = rip;
-
- /* R11 and EFLAGS should already match. */
- assert(ctx->uc_mcontext.gregs[REG_EFL] ==
- ctx->uc_mcontext.gregs[REG_R11]);
-
sethandler(SIGSEGV, sigsegv_for_sigreturn_test, SA_RESETHAND);
+}
- return;
+static void __raise(int sig)
+{
+ do_syscall(__NR_kill, getpid(), sig, 0, 0, 0, 0);
}
static void test_sigreturn_to(unsigned long ip)
{
rip = ip;
printf("[RUN]\tsigreturn to 0x%lx\n", ip);
- raise(SIGUSR1);
+ __raise(SIGUSR1);
}
static jmp_buf jmpbuf;
--
Ammar Faizi
