On January 23, 2023 10:41:20 PM PST, Ammar Faizi ammarfaizi2@gnuweeb.org wrote:
On Mon, Jan 23, 2023 at 10:16:01PM -0800, H. Peter Anvin wrote:
On 1/23/23 18:27, Ammar Faizi wrote:
Test that:
- "syscall" in a FRED system doesn't clobber %rcx and %r11.
- "syscall" in a non-FRED system sets %rcx=%rip and %r11=%rflags.
Test them out with a trivial system call like __NR_getppid and friends which are extremely likely to return with SYSRET on an IDT system; check that it returns a nonnegative value and then save the result.
"Nonnegative" here should be "valid"; it is an implementation detail that the error value is -1.
Copy-paste error, will fix that!
However, you are not checking that you don't get a mix of REGS_SAVED and REGS_SYSRET, which is a major part of the point.
Good point!
What do you think of adding this on top of patch #1?
diff --git a/tools/testing/selftests/x86/sysret_rip.c b/tools/testing/selftests/x86/sysret_rip.c index 75c72d34dbc5840c..3da827713831acbc 100644 --- a/tools/testing/selftests/x86/sysret_rip.c +++ b/tools/testing/selftests/x86/sysret_rip.c @@ -47,11 +47,14 @@ static const unsigned long rcx_sentinel = 0x5ca1ab1e0b57ac1e; static const unsigned long rflags_sentinel = 0x200a93;
enum regs_ok {
- REGS_ERROR = -1, /* Invalid register contents */
- REGS_SAVED = 0, /* Registers properly preserved */
- REGS_SYSRET = 1 /* Registers match syscall/sysret */
- REGS_INIT_VAL = -2, /* For init value checker, never returned */
- REGS_ERROR = -1, /* Invalid register contents */
- REGS_SAVED = 0, /* Registers properly preserved */
- REGS_SYSRET = 1 /* Registers match syscall/sysret */
};
+static enum regs_ok regs_ok_state = REGS_INIT_VAL;
/*
- Returns:
- 0 = %rcx and %r11 preserved.
@@ -86,6 +89,7 @@ static long do_syscall(long nr_syscall, unsigned long arg1, unsigned long arg2, register unsigned long r9 asm("%r9"); register void *rsp asm("%rsp"); unsigned long rcx, rbx;
enum regs_ok ret;
r11 = r11_sentinel; rcx = rcx_sentinel;
@@ -124,7 +128,14 @@ static long do_syscall(long nr_syscall, unsigned long arg1, unsigned long arg2, * - "syscall" in a non-FRED system sets %rcx=%rip and %r11=%rflags. * */
- assert(check_regs_result(r11, rcx, rbx) != REGS_ERROR);
- ret = check_regs_result(r11, rcx, rbx);
- assert(ret != REGS_ERROR);
- if (regs_ok_state == REGS_INIT_VAL)
regs_ok_state = ret;- else
assert(ret == regs_ok_state);- return nr_syscall;
}
Works for me, although I would call it REGS_UNDEFINED myself.