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SubjectRe: [PATCH v2 1/1] arm64: make a single hook to syscall_trace() for all syscall features
On 02/26/2014 12:00 AM, Will Deacon wrote:
> On Tue, Feb 25, 2014 at 09:14:43AM +0000, AKASHI Takahiro wrote:
>> Currently syscall_trace() is called only for ptrace.
>> With additional TIF_xx flags defined, it is now called in all the cases
>> of audit, ftrace and seccomp in addition to ptrace.
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>> Acked-by: Richard Guy Briggs <rgb@redhat.com>
>> ---
>> arch/arm64/include/asm/thread_info.h | 13 ++++++++++
>> arch/arm64/kernel/entry.S | 5 ++--
>> arch/arm64/kernel/ptrace.c | 45 +++++++++++++++++-----------------
>> 3 files changed, 38 insertions(+), 25 deletions(-)

[...]

>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index 6a8928b..c70133e 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -1062,31 +1062,30 @@ asmlinkage int syscall_trace(int dir, struct pt_regs *regs)
>> {
>> unsigned long saved_reg;
>>
>> - if (!test_thread_flag(TIF_SYSCALL_TRACE))
>> - return regs->syscallno;
>> -
>> - if (is_compat_task()) {
>> - /* AArch32 uses ip (r12) for scratch */
>> - saved_reg = regs->regs[12];
>> - regs->regs[12] = dir;
>> - } else {
>> - /*
>> - * Save X7. X7 is used to denote syscall entry/exit:
>> - * X7 = 0 -> entry, = 1 -> exit
>> - */
>> - saved_reg = regs->regs[7];
>> - regs->regs[7] = dir;
>> - }
>> + if (test_thread_flag(TIF_SYSCALL_TRACE)) {
>> + if (is_compat_task()) {
>> + /* AArch32 uses ip (r12) for scratch */
>> + saved_reg = regs->regs[12];
>> + regs->regs[12] = dir;
>> + } else {
>> + /*
>> + * Save X7. X7 is used to denote syscall entry/exit:
>> + * X7 = 0 -> entry, = 1 -> exit
>> + */
>> + saved_reg = regs->regs[7];
>> + regs->regs[7] = dir;
>> + }
>>
>> - if (dir)
>> - tracehook_report_syscall_exit(regs, 0);
>> - else if (tracehook_report_syscall_entry(regs))
>> - regs->syscallno = ~0UL;
>> + if (dir)
>> + tracehook_report_syscall_exit(regs, 0);
>> + else if (tracehook_report_syscall_entry(regs))
>> + regs->syscallno = ~0UL;
>>
>> - if (is_compat_task())
>> - regs->regs[12] = saved_reg;
>> - else
>> - regs->regs[7] = saved_reg;
>> + if (is_compat_task())
>> + regs->regs[12] = saved_reg;
>> + else
>> + regs->regs[7] = saved_reg;
>> + }
>
> Aren't these changes (to ptrace.c) just a giant NOP?

Umm, the purpose of this big "if" is to run the code only if TIF_SYSCALL_TRACE is set,
and to make it easy to add additional hooks, audit and ftrace, around tracehook_report_*()
later on.

-Takahiro AKASHI

> Will
>


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