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SubjectRe: [PATCH v3 3/3] arm64: audit: Add audit hook in ptrace/syscall_trace
On 02/05/2014 02:31 AM, Will Deacon wrote:
> On Mon, Feb 03, 2014 at 06:56:30AM +0000, AKASHI Takahiro wrote:
>> This patch adds auditing functions on entry to or exit from
>> every system call invocation.
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>> ---
>> arch/arm64/include/asm/thread_info.h | 1 +
>> arch/arm64/kernel/entry.S | 3 +++
>> arch/arm64/kernel/ptrace.c | 10 ++++++++++
>> 3 files changed, 14 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
>> index 720e70b..7468388 100644
>> --- a/arch/arm64/include/asm/thread_info.h
>> +++ b/arch/arm64/include/asm/thread_info.h
>> @@ -101,6 +101,7 @@ static inline struct thread_info *current_thread_info(void)
>> #define TIF_NEED_RESCHED 1
>> #define TIF_NOTIFY_RESUME 2 /* callback before returning to user */
>> #define TIF_SYSCALL_TRACE 8
>> +#define TIF_SYSCALL_AUDIT 9
>> #define TIF_POLLING_NRFLAG 16
>> #define TIF_MEMDIE 18 /* is terminating due to OOM killer */
>> #define TIF_FREEZE 19
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index 827cbad..83c4b29 100644
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -630,6 +630,9 @@ el0_svc_naked: // compat entry point
>> get_thread_info tsk
>> ldr x16, [tsk, #TI_FLAGS] // check for syscall tracing
>> tbnz x16, #TIF_SYSCALL_TRACE, __sys_trace // are we tracing syscalls?
>> +#ifdef CONFIG_AUDITSYSCALL
>> + tbnz x16, #TIF_SYSCALL_AUDIT, __sys_trace // auditing syscalls?
>> +#endif
>
> Could we avoid the back-to-back tbnz instructions with a single mask? It's
> not obvious that it will end up any better, but it would be good to know.

When first implementing ftrace support, TIF_SYSCALL_TRACEPOINT is defined as 10
and 'tst' instruction doesn't allow the following code:
tst x16, #(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_TRACEPOINT)

That is why I've used "back-to-back" tbnz since then, but now that I'm going to
submit ftrace, audit and later seccomp, I will replace it with:
#define TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE|TRACEPOINT|AUDIT|SECCOMP)

tst x16, #TIF_SYSCALL_WORK
b.ne __syscall_trace


>> adr lr, ret_fast_syscall // return address
>> cmp scno, sc_nr // check upper syscall limit
>> b.hs ni_sys
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index 6777a21..75a3f23 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -19,6 +19,7 @@
>> * along with this program. If not, see <http://www.gnu.org/licenses/>.
>> */
>>
>> +#include <linux/audit.h>
>> #include <linux/kernel.h>
>> #include <linux/sched.h>
>> #include <linux/mm.h>
>> @@ -38,6 +39,7 @@
>> #include <asm/compat.h>
>> #include <asm/debug-monitors.h>
>> #include <asm/pgtable.h>
>> +#include <asm/syscall.h>
>> #include <asm/traps.h>
>> #include <asm/system_misc.h>
>>
>> @@ -1064,6 +1066,14 @@ asmlinkage int syscall_trace(int dir, struct pt_regs *regs)
>> {
>> unsigned long saved_reg;
>>
>> + if (dir)
>> + audit_syscall_exit(regs);
>> + else
>> + audit_syscall_entry(syscall_get_arch(current, regs),
>> + (int)regs->syscallno,
>> + regs->orig_x0, regs->regs[1],
>> + regs->regs[2], regs->regs[3]);
>> +
>
> Do we really want to perform the audit checks before the tracehook calls?
> Remember that the latter can rewrite all of the registers.

OK. I will change the code to make calls in the following order:
On entry,
*secure_computing
*tracehook_report_syscall(ENTER)
*trace_sys_enter
*audit_syscall_entry
On exit,
*audit_syscall_exit
*trace_sys_exit
*tracehook_report_syscall(EXIT)
The order here is the exact same as on x86, but such change might
decrease the readability in syscall_trace().

Thanks,
-Takahiro AKASHI

> Will
>


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