Messages in this thread | | | Date | Wed, 8 Oct 2014 10:30:18 -0500 | Subject | Re: [PATCH v7 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL | From | Kees Cook <> |
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On Wed, Oct 8, 2014 at 9:13 AM, Will Deacon <will.deacon@arm.com> wrote: > Hi Akashi, > > On Thu, Oct 02, 2014 at 10:46:11AM +0100, AKASHI Takahiro wrote: >> To allow tracer to be able to change/skip a system call by re-writing >> a syscall number, there are several approaches: >> >> (1) modify x8 register with ptrace(PTRACE_SETREGSET), and handle this case >> later on in syscall_trace_enter(), or >> (2) support ptrace(PTRACE_SET_SYSCALL) as on arm >> >> Thinking of the fact that user_pt_regs doesn't expose 'syscallno' to >> tracer as well as that secure_computing() expects a changed syscall number >> to be visible, especially case of -1, before this function returns in >> syscall_trace_enter(), we'd better take (2). >> >> Reviewed-by: Kees Cook <keescook@chromium.org> >> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> >> --- >> arch/arm64/include/uapi/asm/ptrace.h | 1 + >> arch/arm64/kernel/ptrace.c | 14 +++++++++++++- >> 2 files changed, 14 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h >> index 6913643..49c6174 100644 >> --- a/arch/arm64/include/uapi/asm/ptrace.h >> +++ b/arch/arm64/include/uapi/asm/ptrace.h >> @@ -23,6 +23,7 @@ >> >> #include <asm/hwcap.h> >> >> +#define PTRACE_SET_SYSCALL 23 >> >> /* >> * PSR bits >> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c >> index fe63ac5..2842f9f 100644 >> --- a/arch/arm64/kernel/ptrace.c >> +++ b/arch/arm64/kernel/ptrace.c >> @@ -1082,7 +1082,19 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task) >> long arch_ptrace(struct task_struct *child, long request, >> unsigned long addr, unsigned long data) >> { >> - return ptrace_request(child, request, addr, data); >> + int ret; >> + >> + switch (request) { >> + case PTRACE_SET_SYSCALL: >> + task_pt_regs(child)->syscallno = data; >> + ret = 0; >> + break; >> + default: >> + ret = ptrace_request(child, request, addr, data); >> + break; >> + } >> + >> + return ret; >> } > > I still don't understand why this needs to be in arch-specific code. Can't > we implement this in generic code and get architectures to implement > something like syscall_set_nr if they want the generic interface?
Personally, I'd rather see this land as-is in the arm64 tree, and then later optimize PTRACE_SET_SYSCALL out of arm/ and arm64/, especially since only these architectures implement this at the moment.
This is my plan for the asm-generic seccomp.h too -- I'd rather avoid touching other architectures in this series, as it's easier to review this way. Then we can optimize the code in a separate series, which will have those changes isolated, etc.
-Kees
-- Kees Cook Chrome OS Security
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