From: AKASHI Takahiro <takahiro.akashi@linaro.org>
To: Andy Lutomirski <luto@amacapital.net>,
wad@chromium.org, catalin.marinas@arm.com, will.deacon@arm.com,
keescook@chromium.org
Cc: dsaxena@linaro.org, linux-arm-kernel@lists.infradead.org,
linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations
Date: Thu, 24 Jul 2014 14:57:11 +0900 [thread overview]
Message-ID: <53D0A037.2060308@linaro.org> (raw)
In-Reply-To: <53D08358.4020902@amacapital.net>
On 07/24/2014 12:54 PM, Andy Lutomirski wrote:
> On 07/22/2014 02:14 AM, AKASHI Takahiro wrote:
>> Arm64 holds a syscall number in w8(x8) register. Ptrace tracer may change
>> its value either to:
>> * any valid syscall number to alter a system call, or
>> * -1 to skip a system call
>>
>> This patch implements this behavior by reloading that value into syscallno
>> in struct pt_regs after tracehook_report_syscall_entry() or
>> secure_computing(). In case of '-1', a return value of system call can also
>> be changed by the tracer setting the value to x0 register, and so
>> sys_ni_nosyscall() should not be called.
>>
>> See also:
>> 42309ab4, ARM: 8087/1: ptrace: reload syscall number after
>> secure_computing() check
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>> ---
>> arch/arm64/kernel/entry.S | 2 ++
>> arch/arm64/kernel/ptrace.c | 13 +++++++++++++
>> 2 files changed, 15 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index 5141e79..de8bdbc 100644
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -628,6 +628,8 @@ ENDPROC(el0_svc)
>> __sys_trace:
>> mov x0, sp
>> bl syscall_trace_enter
>> + cmp w0, #-1 // skip syscall?
>> + b.eq ret_to_user
>
> Does this mean that skipped syscalls will cause exit tracing to be skipped?
Yes. (and I guess yes on arm, too)
> If so, then you risk (at least) introducing
> a nice user-triggerable OOPS if audit is enabled.
Can you please elaborate this?
Since I didn't find any definition of audit's behavior when syscall is
rewritten to -1, I thought it is reasonable to skip "exit tracing" of
"skipped" syscall.
(otherwise, "fake" seems to be more appropriate :)
-Takahiro AKASHI
> This bug existed for *years* on x86_32, and it amazes me that no one
> ever triggered it by accident. (Grr, audit.)
>
> --Andy
next prev parent reply other threads:[~2014-07-24 5:57 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-22 9:14 [PATCH v5 0/3] arm64: Add seccomp support AKASHI Takahiro
2014-07-22 9:14 ` [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations AKASHI Takahiro
2014-07-22 20:15 ` Kees Cook
2014-07-23 7:03 ` AKASHI Takahiro
2014-07-23 8:25 ` Will Deacon
2014-07-23 9:09 ` AKASHI Takahiro
2014-07-23 15:13 ` Kees Cook
2014-07-24 3:54 ` Andy Lutomirski
2014-07-24 5:57 ` AKASHI Takahiro [this message]
2014-07-24 15:01 ` Andy Lutomirski
2014-07-25 10:36 ` AKASHI Takahiro
2014-07-25 11:03 ` Will Deacon
2014-07-29 6:49 ` AKASHI Takahiro
2014-07-29 13:26 ` Will Deacon
2014-07-22 9:14 ` [PATCH v5 2/3] asm-generic: Add generic seccomp.h for secure computing mode 1 AKASHI Takahiro
2014-07-24 3:40 ` Andy Lutomirski
2014-07-24 4:41 ` Kees Cook
2014-07-24 5:17 ` AKASHI Takahiro
2014-07-24 14:57 ` Andy Lutomirski
2014-07-25 8:52 ` AKASHI Takahiro
2014-07-22 9:14 ` [PATCH v5 3/3] arm64: Add seccomp support AKASHI Takahiro
2014-07-24 3:52 ` Andy Lutomirski
2014-07-24 5:40 ` AKASHI Takahiro
2014-07-24 15:00 ` Andy Lutomirski
2014-07-24 15:16 ` Catalin Marinas
2014-07-25 9:37 ` AKASHI Takahiro
2014-08-05 15:08 ` Kees Cook
2014-08-08 7:35 ` AKASHI Takahiro
2014-08-11 9:24 ` Will Deacon
2014-08-12 6:57 ` AKASHI Takahiro
2014-08-12 9:40 ` Will Deacon
2014-08-12 11:17 ` AKASHI Takahiro
2014-08-15 14:33 ` Will Deacon
2014-07-22 20:16 ` [PATCH v5 0/3] " Kees Cook
2014-07-23 7:09 ` AKASHI Takahiro
2014-07-23 15:36 ` Kees Cook
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