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Date: Fri, 22 Aug 2014 09:19:13 +0900 From: AKASHI Takahiro <takahiro.akashi@...aro.org> To: Kees Cook <keescook@...omium.org> CC: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Deepak Saxena <dsaxena@...aro.org>, arndb@...db.de, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, linaro-kernel@...ts.linaro.org, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v6 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL On 08/22/2014 01:47 AM, Kees Cook wrote: > On Thu, Aug 21, 2014 at 3:56 AM, AKASHI Takahiro > <takahiro.akashi@...aro.org> 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). >> >> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org> > > Thanks, I like having this on both arm and arm64. Yeah, having this simplified the code of syscall_trace_enter() a bit, but also imposes some restriction on arm64, too. > I wonder if other archs should add this option too. Do you think so? I assumed that SET_SYSCALL is to be avoided if possible. I also think that SET_SYSCALL should take an extra argument for a return value just in case of -1 (or we have SKIP_SYSCALL?). -Takahiro AKASHI > Reviewed-by: Kees Cook <keescook@...omium.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 0310811..8876049 100644 >> --- a/arch/arm64/kernel/ptrace.c >> +++ b/arch/arm64/kernel/ptrace.c >> @@ -1077,7 +1077,19 @@ 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; >> } >> >> enum ptrace_syscall_dir { >> -- >> 1.7.9.5 >> > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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