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.akashi@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);