From: AKASHI Takahiro <takahiro.akashi@linaro.org> To: Will Deacon <will.deacon@arm.com> Cc: Kees Cook <keescook@chromium.org>, Catalin Marinas <Catalin.Marinas@arm.com>, Deepak Saxena <dsaxena@linaro.org>, "arndb@arndb.de" <arndb@arndb.de>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "linaro-kernel@lists.linaro.org" <linaro-kernel@lists.linaro.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [PATCH v6 2/6] arm64: ptrace: allow tracer to skip a system call Date: Wed, 27 Aug 2014 14:55:46 +0900 [thread overview] Message-ID: <53FD72E2.4020103@linaro.org> (raw) In-Reply-To: <20140826175128.GD23445@arm.com> On 08/27/2014 02:51 AM, Will Deacon wrote: > On Fri, Aug 22, 2014 at 01:35:17AM +0100, AKASHI Takahiro wrote: >> On 08/22/2014 02:08 AM, Kees Cook wrote: >>> On Thu, Aug 21, 2014 at 3:56 AM, AKASHI Takahiro >>> <takahiro.akashi@linaro.org> wrote: >>>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c >>>> index 8876049..c54dbcc 100644 >>>> --- a/arch/arm64/kernel/ptrace.c >>>> +++ b/arch/arm64/kernel/ptrace.c >>>> @@ -1121,9 +1121,29 @@ static void tracehook_report_syscall(struct pt_regs *regs, >>>> >>>> asmlinkage int syscall_trace_enter(struct pt_regs *regs) >>>> { >>>> + unsigned int saved_syscallno = regs->syscallno; >>>> + >>>> if (test_thread_flag(TIF_SYSCALL_TRACE)) >>>> tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER); >>>> >>>> + if (IS_SKIP_SYSCALL(regs->syscallno)) { >>>> + /* >>>> + * RESTRICTION: we can't modify a return value of user >>>> + * issued syscall(-1) here. In order to ease this flavor, >>>> + * we need to treat whatever value in x0 as a return value, >>>> + * but this might result in a bogus value being returned. >>>> + */ >>>> + /* >>>> + * NOTE: syscallno may also be set to -1 if fatal signal is >>>> + * detected in tracehook_report_syscall_entry(), but since >>>> + * a value set to x0 here is not used in this case, we may >>>> + * neglect the case. >>>> + */ >>>> + if (!test_thread_flag(TIF_SYSCALL_TRACE) || >>>> + (IS_SKIP_SYSCALL(saved_syscallno))) >>>> + regs->regs[0] = -ENOSYS; >>>> + } >>>> + >>> >>> I don't have a runtime environment yet for arm64, so I can't test this >>> directly myself, so I'm just trying to eyeball this. :) >>> >>> Once the seccomp logic is added here, I don't think using -2 as a >>> special value will work. Doesn't this mean the Oops is possible by the >>> user issuing a "-2" syscall? As in, if TIF_SYSCALL_WORK is set, and >>> the user passed -2 as the syscall, audit will be called only on entry, >>> and then skipped on exit? >> >> Oops, you're absolutely right. I didn't think of this case. >> syscall_trace_enter() should not return a syscallno directly, but always >> return -1 if syscallno < 0. (except when secure_computing() returns with -1) >> This also implies that tracehook_report_syscall() should also have a return value. >> >> Will, is this fine with you? > > Well, the first thing that jumps out at me is why this is being done > completely differently for arm64 and arm. I thought adding the new ptrace > requests would reconcile the differences? I'm not sure what portion of my code you mentioned as "completely different", but 1) setting x0 to -ENOSYS is necessary because, otherwise, user-issued syscall(-1) will return a bogus value when audit tracing is on. Please note that, on arm, not traced traced ------ ------ syscall(-1) aborted OOPs(BUG_ON) syscall(-3000) aborted aborted syscall(1000) ENOSYS ENOSYS So, anyhow, its a bit difficult and meaningless to mimic these invalid cases. 2) branching a new label, syscall_trace_return_skip (see entry.S), after syscall_trace_enter() is necessary in order to avoid OOPS in audit_syscall_enter() as we discussed. Did I make it clear? -Takahiro AKASHI > Will >
WARNING: multiple messages have this Message-ID (diff)
From: takahiro.akashi@linaro.org (AKASHI Takahiro) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH v6 2/6] arm64: ptrace: allow tracer to skip a system call Date: Wed, 27 Aug 2014 14:55:46 +0900 [thread overview] Message-ID: <53FD72E2.4020103@linaro.org> (raw) In-Reply-To: <20140826175128.GD23445@arm.com> On 08/27/2014 02:51 AM, Will Deacon wrote: > On Fri, Aug 22, 2014 at 01:35:17AM +0100, AKASHI Takahiro wrote: >> On 08/22/2014 02:08 AM, Kees Cook wrote: >>> On Thu, Aug 21, 2014 at 3:56 AM, AKASHI Takahiro >>> <takahiro.akashi@linaro.org> wrote: >>>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c >>>> index 8876049..c54dbcc 100644 >>>> --- a/arch/arm64/kernel/ptrace.c >>>> +++ b/arch/arm64/kernel/ptrace.c >>>> @@ -1121,9 +1121,29 @@ static void tracehook_report_syscall(struct pt_regs *regs, >>>> >>>> asmlinkage int syscall_trace_enter(struct pt_regs *regs) >>>> { >>>> + unsigned int saved_syscallno = regs->syscallno; >>>> + >>>> if (test_thread_flag(TIF_SYSCALL_TRACE)) >>>> tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER); >>>> >>>> + if (IS_SKIP_SYSCALL(regs->syscallno)) { >>>> + /* >>>> + * RESTRICTION: we can't modify a return value of user >>>> + * issued syscall(-1) here. In order to ease this flavor, >>>> + * we need to treat whatever value in x0 as a return value, >>>> + * but this might result in a bogus value being returned. >>>> + */ >>>> + /* >>>> + * NOTE: syscallno may also be set to -1 if fatal signal is >>>> + * detected in tracehook_report_syscall_entry(), but since >>>> + * a value set to x0 here is not used in this case, we may >>>> + * neglect the case. >>>> + */ >>>> + if (!test_thread_flag(TIF_SYSCALL_TRACE) || >>>> + (IS_SKIP_SYSCALL(saved_syscallno))) >>>> + regs->regs[0] = -ENOSYS; >>>> + } >>>> + >>> >>> I don't have a runtime environment yet for arm64, so I can't test this >>> directly myself, so I'm just trying to eyeball this. :) >>> >>> Once the seccomp logic is added here, I don't think using -2 as a >>> special value will work. Doesn't this mean the Oops is possible by the >>> user issuing a "-2" syscall? As in, if TIF_SYSCALL_WORK is set, and >>> the user passed -2 as the syscall, audit will be called only on entry, >>> and then skipped on exit? >> >> Oops, you're absolutely right. I didn't think of this case. >> syscall_trace_enter() should not return a syscallno directly, but always >> return -1 if syscallno < 0. (except when secure_computing() returns with -1) >> This also implies that tracehook_report_syscall() should also have a return value. >> >> Will, is this fine with you? > > Well, the first thing that jumps out at me is why this is being done > completely differently for arm64 and arm. I thought adding the new ptrace > requests would reconcile the differences? I'm not sure what portion of my code you mentioned as "completely different", but 1) setting x0 to -ENOSYS is necessary because, otherwise, user-issued syscall(-1) will return a bogus value when audit tracing is on. Please note that, on arm, not traced traced ------ ------ syscall(-1) aborted OOPs(BUG_ON) syscall(-3000) aborted aborted syscall(1000) ENOSYS ENOSYS So, anyhow, its a bit difficult and meaningless to mimic these invalid cases. 2) branching a new label, syscall_trace_return_skip (see entry.S), after syscall_trace_enter() is necessary in order to avoid OOPS in audit_syscall_enter() as we discussed. Did I make it clear? -Takahiro AKASHI > Will >
next prev parent reply other threads:[~2014-08-27 5:55 UTC|newest] Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-08-21 8:56 [PATCH v6 0/6] arm64: add seccomp support AKASHI Takahiro 2014-08-21 8:56 ` AKASHI Takahiro 2014-08-21 8:56 ` [PATCH v6 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL AKASHI Takahiro 2014-08-21 8:56 ` AKASHI Takahiro 2014-08-21 16:47 ` Kees Cook 2014-08-21 16:47 ` Kees Cook 2014-08-22 0:19 ` AKASHI Takahiro 2014-08-22 0:19 ` AKASHI Takahiro 2014-08-26 17:46 ` Will Deacon 2014-08-26 17:46 ` Will Deacon 2014-08-27 5:32 ` AKASHI Takahiro 2014-08-27 5:32 ` AKASHI Takahiro 2014-09-03 18:34 ` Kees Cook 2014-09-03 18:34 ` Kees Cook 2014-08-21 8:56 ` [PATCH v6 2/6] arm64: ptrace: allow tracer to skip a system call AKASHI Takahiro 2014-08-21 8:56 ` AKASHI Takahiro 2014-08-21 17:08 ` Kees Cook 2014-08-21 17:08 ` Kees Cook 2014-08-22 0:35 ` AKASHI Takahiro 2014-08-22 0:35 ` AKASHI Takahiro 2014-08-26 17:51 ` Will Deacon 2014-08-26 17:51 ` Will Deacon 2014-08-27 5:55 ` AKASHI Takahiro [this message] 2014-08-27 5:55 ` AKASHI Takahiro 2014-09-01 11:37 ` Will Deacon 2014-09-01 11:37 ` Will Deacon 2014-09-02 7:58 ` AKASHI Takahiro 2014-09-02 7:58 ` AKASHI Takahiro 2014-09-01 11:47 ` Russell King - ARM Linux 2014-09-01 11:47 ` Russell King - ARM Linux 2014-09-02 8:47 ` AKASHI Takahiro 2014-09-02 8:47 ` AKASHI Takahiro 2014-09-02 9:16 ` Russell King - ARM Linux 2014-09-02 9:16 ` Russell King - ARM Linux 2014-09-02 9:31 ` Russell King - ARM Linux 2014-09-02 9:31 ` Russell King - ARM Linux 2014-09-05 10:08 ` AKASHI Takahiro 2014-09-05 10:08 ` AKASHI Takahiro 2014-10-01 11:08 ` AKASHI Takahiro 2014-10-01 11:08 ` AKASHI Takahiro 2014-10-03 15:23 ` Will Deacon 2014-10-03 15:23 ` Will Deacon 2014-10-06 8:04 ` AKASHI Takahiro 2014-10-06 8:04 ` AKASHI Takahiro 2014-08-21 8:56 ` [PATCH v6 3/6] asm-generic: add generic seccomp.h for secure computing mode 1 AKASHI Takahiro 2014-08-21 8:56 ` AKASHI Takahiro 2014-08-21 17:51 ` Kees Cook 2014-08-21 17:51 ` Kees Cook 2014-08-22 0:38 ` AKASHI Takahiro 2014-08-22 0:38 ` AKASHI Takahiro 2014-08-21 8:56 ` [PATCH v6 4/6] arm64: add seccomp syscall for compat task AKASHI Takahiro 2014-08-21 8:56 ` AKASHI Takahiro 2014-08-21 17:52 ` Kees Cook 2014-08-21 17:52 ` Kees Cook 2014-08-22 0:39 ` AKASHI Takahiro 2014-08-22 0:39 ` AKASHI Takahiro 2014-08-26 17:53 ` Will Deacon 2014-08-26 17:53 ` Will Deacon 2014-08-27 5:57 ` AKASHI Takahiro 2014-08-27 5:57 ` AKASHI Takahiro 2014-08-21 8:56 ` [PATCH v6 5/6] arm64: add SIGSYS siginfo " AKASHI Takahiro 2014-08-21 8:56 ` AKASHI Takahiro 2014-08-21 17:54 ` Kees Cook 2014-08-21 17:54 ` Kees Cook 2014-08-22 0:44 ` AKASHI Takahiro 2014-08-22 0:44 ` AKASHI Takahiro 2014-08-26 17:55 ` Will Deacon 2014-08-26 17:55 ` Will Deacon 2014-08-27 5:58 ` AKASHI Takahiro 2014-08-27 5:58 ` AKASHI Takahiro 2014-08-21 8:56 ` [PATCH v6 6/6] arm64: add seccomp support AKASHI Takahiro 2014-08-21 8:56 ` AKASHI Takahiro
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