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.aka...@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
adr lr, __sys_trace_return // return address
uxtw scno, w0 // syscall number (possibly new)
mov x1, sp // pointer to regs
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 70526cf..100d7d1 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -21,6 +21,7 @@
#include <linux/audit.h>
#include <linux/compat.h>
+#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/mm.h>
@@ -1109,9 +1110,21 @@ static void tracehook_report_syscall(struct pt_regs
*regs,
asmlinkage int syscall_trace_enter(struct pt_regs *regs)
{
+ unsigned long saved_x0, saved_x8;
+
+ saved_x0 = regs->regs[0];
+ saved_x8 = regs->regs[8];
+
if (test_thread_flag(TIF_SYSCALL_TRACE))
tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
+ regs->syscallno = regs->regs[8];
+ if ((long)regs->syscallno == ~0UL) { /* skip this syscall */
+ regs->regs[8] = saved_x8;
+ if (regs->regs[0] == saved_x0) /* not changed by user */
+ regs->regs[0] = -ENOSYS;
+ }
+
if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
trace_sys_enter(regs, regs->syscallno);
--
1.7.9.5
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
