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Subject[PATCH 2/4] arch/arm: move secure_computing into trace
Date
There is very little difference in the TIF_SECCOMP and TIF_SYSCALL_TRACE
path in entry-common.S. In order to add support for
CONFIG_HAVE_ARCH_SECCOMP_FILTER without mangling the assembly too badly,
seccomp was moved into the syscall_trace_enter() handler.

Expanded ptrace_syscall_trace() into both callers to make code more
readable, as requested by Al Viro.

Additionally, the return value for secure_computing() is now checked
and a -1 value will result in the system call being skipped.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/arm/kernel/entry-common.S | 9 ++-------
arch/arm/kernel/ptrace.c | 39 +++++++++++++++++++++++++--------------
2 files changed, 27 insertions(+), 21 deletions(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 3471175..c781012 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -418,13 +418,8 @@ local_restart:
stmdb sp!, {r4, r5} @ push fifth and sixth args

#ifdef CONFIG_SECCOMP
- tst r10, #_TIF_SECCOMP
- beq 1f
- mov r0, scno
- bl __secure_computing
- add r0, sp, #S_R0 + S_OFF @ pointer to regs
- ldmia r0, {r0 - r3} @ have to reload r0 - r3
-1:
+ tst r10, #_TIF_SECCOMP @ is seccomp enabled?
+ bne __sys_trace
#endif

tst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls?
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 739db3a..6b0e14b 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -916,13 +916,15 @@ enum ptrace_syscall_dir {
PTRACE_SYSCALL_EXIT,
};

-static int ptrace_syscall_trace(struct pt_regs *regs, int scno,
- enum ptrace_syscall_dir dir)
+asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
{
unsigned long ip;

current_thread_info()->syscall = scno;

+ if (secure_computing(scno) == -1)
+ return -1;
+
if (!test_thread_flag(TIF_SYSCALL_TRACE))
return scno;

@@ -931,20 +933,13 @@ static int ptrace_syscall_trace(struct pt_regs *regs, int scno,
* IP = 0 -> entry, =1 -> exit
*/
ip = regs->ARM_ip;
- regs->ARM_ip = dir;
-
- if (dir == PTRACE_SYSCALL_EXIT)
- tracehook_report_syscall_exit(regs, 0);
- else if (tracehook_report_syscall_entry(regs))
+ regs->ARM_ip = PTRACE_SYSCALL_ENTER;
+ if (tracehook_report_syscall_entry(regs))
current_thread_info()->syscall = -1;
-
regs->ARM_ip = ip;
- return current_thread_info()->syscall;
-}

-asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
-{
- scno = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_ENTER);
+ scno = current_thread_info()->syscall;
+
if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
trace_sys_enter(regs, scno);
audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1,
@@ -954,7 +949,23 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)

asmlinkage int syscall_trace_exit(struct pt_regs *regs, int scno)
{
- scno = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_EXIT);
+ unsigned long ip;
+
+ current_thread_info()->syscall = scno;
+
+ if (!test_thread_flag(TIF_SYSCALL_TRACE))
+ return scno;
+
+ /*
+ * IP is used to denote syscall entry/exit:
+ * IP = 0 -> entry, =1 -> exit
+ */
+ ip = regs->ARM_ip;
+ regs->ARM_ip = PTRACE_SYSCALL_EXIT;
+ tracehook_report_syscall_exit(regs, 0);
+ regs->ARM_ip = ip;
+
+ scno = current_thread_info()->syscall;
if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
trace_sys_exit(regs, scno);
audit_syscall_exit(regs);
--
1.7.9.5


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