linux-kernel - [RFC PATCH v2 2/2] selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`

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Message-Id: <20230124022729.596997-3-ammarfaizi2@gnuweeb.org>
Date:   Tue, 24 Jan 2023 09:27:29 +0700
From:   Ammar Faizi <ammarfaizi2@...weeb.org>
To:     "H. Peter Anvin" <hpa@...or.com>, x86 Mailing List <x86@...nel.org>
Cc:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xin Li <xin3.li@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Shuah Khan <shuah@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linux Kselftest Mailing List 
        <linux-kselftest@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH v2 2/2] selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`

From: Ammar Faizi <ammarfaizi2@...weeb.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; check
that it returns a nonnegative value and then save the result.

Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-786b55054126@zytor.com
Co-developed-by: "H. Peter Anvin" <hpa@...or.com>
Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.org>
---

Need hpa's sign off.

 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 550bc4e69ac46997..75c72d34dbc5840c 100644
--- a/tools/testing/selftests/x86/sysret_rip.c
+++ b/tools/testing/selftests/x86/sysret_rip.c
@@ -252,8 +252,17 @@ 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