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From:   Kees Cook <keescook@chromium.org>
To:     linux-kernel@vger.kernel.org
Cc:     Kees Cook <keescook@chromium.org>,
        Thadeu Lima de Souza Cascardo <cascardo@canonical.com>,
        Max Filippov <jcmvbkbc@gmail.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
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        Andy Lutomirski <luto@amacapital.net>,
        Will Drewry <wad@chromium.org>,
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        linux-xtensa@linux-xtensa.org,
        linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org
Subject: [PATCH 10/15] selftests/seccomp: Avoid redundant register flushes
Date:   Sat, 12 Sep 2020 04:08:15 -0700
Message-Id: <20200912110820.597135-11-keescook@chromium.org>
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When none of the registers have changed, don't flush them back. This can
happen if the architecture uses a non-register way to change the syscall
(e.g. arm64) , and a return value hasn't been written.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index d9346121b89b..2790d9cd50f4 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -1859,11 +1859,12 @@ int get_syscall(struct __test_metadata *_metadata, pid_t tracee)
 void change_syscall(struct __test_metadata *_metadata,
 		    pid_t tracee, int syscall, int result)
 {
-	ARCH_REGS regs;
+	ARCH_REGS orig, regs;
 
 	EXPECT_EQ(0, ARCH_GETREGS(regs)) {
 		return;
 	}
+	orig = regs;
 
 	SYSCALL_NUM_SET(regs, syscall);
 
@@ -1876,7 +1877,8 @@ void change_syscall(struct __test_metadata *_metadata,
 #endif
 
 	/* Flush any register changes made. */
-	EXPECT_EQ(0, ARCH_SETREGS(regs));
+	if (memcmp(&orig, &regs, sizeof(orig)) != 0)
+		EXPECT_EQ(0, ARCH_SETREGS(regs));
 }
 
 void tracer_seccomp(struct __test_metadata *_metadata, pid_t tracee,
-- 
2.25.1