From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v9 2/6] arm64: ptrace: allow tracer to skip a system call
Date: Thu, 27 Nov 2014 10:07:22 +0000 [thread overview]
Message-ID: <20141127100722.GB20649@arm.com> (raw)
In-Reply-To: <5476C8C5.4010202@linaro.org>
On Thu, Nov 27, 2014 at 06:46:29AM +0000, AKASHI Takahiro wrote:
> On 11/26/2014 10:02 PM, Will Deacon wrote:
> > On Wed, Nov 26, 2014 at 04:49:47AM +0000, AKASHI Takahiro wrote:
> >> If tracer modifies a syscall number to -1, this traced system call should
> >> be skipped with a return value specified in x0.
> >> This patch implements this semantics.
> >>
> >> Please note:
> >> * syscall entry tracing and syscall exit tracing (ftrace tracepoint and
> >> audit) are always executed, if enabled, even when skipping a system call
> >> (that is, -1).
> >> In this way, we can avoid a potential bug where audit_syscall_entry()
> >> might be called without audit_syscall_exit() at the previous system call
> >> being called, that would cause OOPs in audit_syscall_entry().
> >>
> >> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro•org>
> >> ---
> >> arch/arm64/kernel/entry.S | 10 +++++++++-
> >> 1 file changed, 9 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> >> index 726b910..946ec52 100644
> >> --- a/arch/arm64/kernel/entry.S
> >> +++ b/arch/arm64/kernel/entry.S
> >> @@ -161,6 +161,7 @@
> >> */
> >> sc_nr .req x25 // number of system calls
> >> scno .req x26 // syscall number
> >> +scno_w .req w26 // syscall number (lower 32 bits)
> >> stbl .req x27 // syscall table pointer
> >> tsk .req x28 // current thread_info
> >>
> >> @@ -668,8 +669,14 @@ ENDPROC(el0_svc)
> >> * switches, and waiting for our parent to respond.
> >> */
> >> __sys_trace:
> >> - mov x0, sp
> >> + cmp scno_w, #-1 // set default errno for
> >
> > I hate that we have to use scno_w, but the only alternative I can think of
> > is using w8 directly, which isn't any better and doesn't work for compat.
> > Ho-hum, I guess we'll stick with what you have.
>
> The possible approaches might be:
> * use 32-bit registers for scno & sc_nr and use "sxtw scno, w8," or
> * use an extra reg like
> __sys_trace:
> mov x0, #0xffffffff
or even better: mov w0, #-1
> cmp scno, x0
> b.ne 1f
Good thinking, I prefer that.
Will
next prev parent reply other threads:[~2014-11-27 10:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-26 4:49 [PATCH v9 0/6] arm64: add seccomp support AKASHI Takahiro
2014-11-26 4:49 ` [PATCH v9 1/6] arm64: ptrace: add NT_ARM_SYSTEM_CALL regset AKASHI Takahiro
2014-11-26 12:41 ` Will Deacon
2014-11-27 5:53 ` AKASHI Takahiro
2014-11-27 14:10 ` Will Deacon
2014-11-28 5:25 ` AKASHI Takahiro
2014-11-26 4:49 ` [PATCH v9 2/6] arm64: ptrace: allow tracer to skip a system call AKASHI Takahiro
2014-11-26 13:02 ` Will Deacon
2014-11-27 6:46 ` AKASHI Takahiro
2014-11-27 10:07 ` Will Deacon [this message]
2014-11-26 4:49 ` [PATCH v9 3/6] asm-generic: add generic seccomp.h for secure computing mode 1 AKASHI Takahiro
2014-11-26 4:49 ` [PATCH v9 4/6] arm64: add seccomp syscall for compat task AKASHI Takahiro
2014-11-26 4:49 ` [PATCH v9 5/6] arm64: add SIGSYS siginfo " AKASHI Takahiro
2014-11-26 4:49 ` [PATCH v9 6/6] arm64: add seccomp support AKASHI Takahiro
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