Messages in this thread | | | Date | Thu, 09 Oct 2014 10:55:38 +0900 | From | AKASHI Takahiro <> | Subject | Re: [PATCH v7 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL |
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On 10/09/2014 12:30 AM, Kees Cook wrote: > 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.
+1 :)
-Takahiro AKASHI
> 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 >
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