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.
42309ab4, ARM: 8087/1: ptrace: reload syscall number after
Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
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
@@ -628,6 +628,8 @@ ENDPROC(el0_svc)
mov x0, sp
+ cmp w0, #-1 // skip syscall?
+ b.eq ret_to_user
Does this mean that skipped syscalls will cause exit tracing to be skipped?
a nice user-triggerable OOPS if audit is enabled.
This bug existed for *years* on x86_32, and it amazes me that no one--
ever triggered it by accident. (Grr, audit.)