From: Masami Hiramatsu <mhiramat@kernel.org> To: Robin Murphy <robin.murphy@arm.com> Cc: will@kernel.org, catalin.marinas@arm.com, mhiramat@kernel.org, james.morse@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: kprobes: Drop open-coded exception fixup Date: Mon, 21 Oct 2019 17:49:26 +0900 [thread overview] Message-ID: <20191021174926.10992282af1c36d721a6747d@kernel.org> (raw) In-Reply-To: <e70f7b9de7e601b9e4a6fedad8eaf64d304b1637.1571326276.git.robin.murphy@arm.com> Hi Robin, On Thu, 17 Oct 2019 16:31:42 +0100 Robin Murphy <robin.murphy@arm.com> wrote: > The short-circuit call to fixup_exception() from kprobe_fault_handler() > poses a problem now that the former wants to consume the fault address > too, since the common kprobes API offers us no way to pass it through. > Fortunately, however, it works out to be unnecessary: Thank you for pointing it out! > > - uaccess instructions themselves are not probeable, so at most we > should only ever expect to take a fixable fault from the pre or post > handlers. Right. If it is not fixable, we should handle it as a kernel bug. (to avoid it we can use probe_kernel_read() in kprobe handler) > - the pre and post handler run with preemption disabled, thus for any > fault they may cause, an unhandled return from kprobe_page_fault() > will proceed directly to __do_kernel_fault() thanks to the > faulthandler_disabled() check. OK, this is reasonable. > - __do_kernel_fault() will immediately call fixup_exception() unless > we're in an EL1 instruction abort, and if we've somehow taken one of > those on what we think is the middle of a uaccess routine, then the > world is already very on fire. OK, this looks good to me. Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Thank you! > > Thus we can reasonably drop the call from kprobe_fault_handler() and > leave uaccess fixups to the regular flow. > > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > arch/arm64/kernel/probes/kprobes.c | 7 ------- > 1 file changed, 7 deletions(-) > > diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c > index c4452827419b..422fbd5c6c55 100644 > --- a/arch/arm64/kernel/probes/kprobes.c > +++ b/arch/arm64/kernel/probes/kprobes.c > @@ -334,13 +334,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr) > */ > if (cur->fault_handler && cur->fault_handler(cur, regs, fsr)) > return 1; > - > - /* > - * In case the user-specified fault handler returned > - * zero, try to fix up. > - */ > - if (fixup_exception(regs)) > - return 1; > } > return 0; > } > -- > 2.21.0.dirty > -- Masami Hiramatsu <mhiramat@kernel.org>
WARNING: multiple messages have this Message-ID (diff)
From: Masami Hiramatsu <mhiramat@kernel.org> To: Robin Murphy <robin.murphy@arm.com> Cc: catalin.marinas@arm.com, linux-kernel@vger.kernel.org, james.morse@arm.com, mhiramat@kernel.org, will@kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] arm64: kprobes: Drop open-coded exception fixup Date: Mon, 21 Oct 2019 17:49:26 +0900 [thread overview] Message-ID: <20191021174926.10992282af1c36d721a6747d@kernel.org> (raw) In-Reply-To: <e70f7b9de7e601b9e4a6fedad8eaf64d304b1637.1571326276.git.robin.murphy@arm.com> Hi Robin, On Thu, 17 Oct 2019 16:31:42 +0100 Robin Murphy <robin.murphy@arm.com> wrote: > The short-circuit call to fixup_exception() from kprobe_fault_handler() > poses a problem now that the former wants to consume the fault address > too, since the common kprobes API offers us no way to pass it through. > Fortunately, however, it works out to be unnecessary: Thank you for pointing it out! > > - uaccess instructions themselves are not probeable, so at most we > should only ever expect to take a fixable fault from the pre or post > handlers. Right. If it is not fixable, we should handle it as a kernel bug. (to avoid it we can use probe_kernel_read() in kprobe handler) > - the pre and post handler run with preemption disabled, thus for any > fault they may cause, an unhandled return from kprobe_page_fault() > will proceed directly to __do_kernel_fault() thanks to the > faulthandler_disabled() check. OK, this is reasonable. > - __do_kernel_fault() will immediately call fixup_exception() unless > we're in an EL1 instruction abort, and if we've somehow taken one of > those on what we think is the middle of a uaccess routine, then the > world is already very on fire. OK, this looks good to me. Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Thank you! > > Thus we can reasonably drop the call from kprobe_fault_handler() and > leave uaccess fixups to the regular flow. > > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > arch/arm64/kernel/probes/kprobes.c | 7 ------- > 1 file changed, 7 deletions(-) > > diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c > index c4452827419b..422fbd5c6c55 100644 > --- a/arch/arm64/kernel/probes/kprobes.c > +++ b/arch/arm64/kernel/probes/kprobes.c > @@ -334,13 +334,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr) > */ > if (cur->fault_handler && cur->fault_handler(cur, regs, fsr)) > return 1; > - > - /* > - * In case the user-specified fault handler returned > - * zero, try to fix up. > - */ > - if (fixup_exception(regs)) > - return 1; > } > return 0; > } > -- > 2.21.0.dirty > -- Masami Hiramatsu <mhiramat@kernel.org> _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-10-21 8:49 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-10-17 15:31 [PATCH] arm64: kprobes: Drop open-coded exception fixup Robin Murphy 2019-10-17 15:31 ` Robin Murphy 2019-10-21 8:49 ` Masami Hiramatsu [this message] 2019-10-21 8:49 ` Masami Hiramatsu
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