linux-kernel - [RFC PATCH v1 1/1] arm64: Forget syscall if different from execve*()

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Date:   Mon,  9 May 2022 16:19:57 +0100
From:   Francis Laniel <flaniel@...ux.microsoft.com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-trace-devel@...r.kernel.org,
        Francis Laniel <flaniel@...ux.microsoft.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Mark Brown <broonie@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        Daniel Kiss <daniel.kiss@....com>, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v1 1/1] arm64: Forget syscall if different from execve*()

This patch enables exeve*() to be traced by syscalls:sys_exit_execve
tracepoint.
Previously, calling forget_syscall() would set syscall to -1, which impedes
this tracepoint to prints its information.
So, this patch makes call to forget_syscall() conditional by only calling
it when syscall number is not execve() or execveat().

Signed-off-by: Francis Laniel <flaniel@...ux.microsoft.com>
---
 arch/arm64/include/asm/processor.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 73e38d9a540c..e12ceb363d6a 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -34,6 +34,8 @@
 
 #include <vdso/processor.h>
 
+#include <asm-generic/unistd.h>
+
 #include <asm/alternative.h>
 #include <asm/cpufeature.h>
 #include <asm/hw_breakpoint.h>
@@ -250,8 +252,12 @@ void tls_preserve_current_state(void);
 
 static inline void start_thread_common(struct pt_regs *regs, unsigned long pc)
 {
+	s32 previous_syscall = regs->syscallno;
 	memset(regs, 0, sizeof(*regs));
-	forget_syscall(regs);
+	if (previous_syscall == __NR_execve || previous_syscall == __NR_execveat)
+		regs->syscallno = previous_syscall;
+	else
+		forget_syscall(regs);
 	regs->pc = pc;
 
 	if (system_uses_irq_prio_masking())
-- 
2.25.1