[v3] selftests/x86: sysret_rip update for FRED system

[RFC PATCH v3 2/2] selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`

Posted by Ammar Faizi 2 years, 7 months ago

From: Ammar Faizi <ammarfaizi2@gnuweeb.org>

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.

Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-786b55054126@zytor.com
Co-developed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Acked-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
 tools/testing/selftests/x86/sysret_rip.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/testing/selftests/x86/sysret_rip.c b/tools/testing/selftests/x86/sysret_rip.c
index b0d271c19ddd7834..bf90fac95a264e2d 100644
--- a/tools/testing/selftests/x86/sysret_rip.c
+++ b/tools/testing/selftests/x86/sysret_rip.c
@@ -267,8 +267,17 @@ static void test_syscall_fallthrough_to(unsigned long ip)
 	printf("[OK]\tWe survived\n");
 }
 
+static void test_syscall_rcx_r11(void)
+{
+	do_syscall(__NR_getpid, 0, 0, 0, 0, 0, 0);
+	do_syscall(__NR_gettid, 0, 0, 0, 0, 0, 0);
+	do_syscall(__NR_getppid, 0, 0, 0, 0, 0, 0);
+}
+
 int main()
 {
+	test_syscall_rcx_r11();
+
 	/*
 	 * When the kernel returns from a slow-path syscall, it will
 	 * detect whether SYSRET is appropriate.  If it incorrectly
-- 
Ammar Faizi

Re: [RFC PATCH v3 2/2] selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`

Posted by H. Peter Anvin 2 years, 7 months ago


On 1/24/23 02:09, Ammar Faizi wrote:
> From: Ammar Faizi <ammarfaizi2@gnuweeb.org>
> 
> 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.
> 
> Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-786b55054126@zytor.com
> Co-developed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> Acked-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>

Add to the description that the purpose of this is to ensure that 
various system calls are *consistent*, as per the comment immediately 
below your code.

	-hpa

Re: [RFC PATCH v3 2/2] selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`

Posted by Ammar Faizi 2 years, 7 months ago

On Tue, Jan 24, 2023 at 12:59:23PM -0800, H. Peter Anvin wrote:
> 
> 
> On 1/24/23 02:09, Ammar Faizi wrote:
> > From: Ammar Faizi <ammarfaizi2@gnuweeb.org>
> > 
> > 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.
> > 
> > Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-786b55054126@zytor.com
> > Co-developed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> > Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> > Acked-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> > Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
> 
> Add to the description that the purpose of this is to ensure that various
> system calls are *consistent*, as per the comment immediately below your
> code.

Added in v4.

-- 
Ammar Faizi