From: Robin Murphy <robin.murphy@arm.com>
To: will@kernel.org, catalin.marinas@arm.com
Cc: james.morse@arm.com, mhiramat@kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: [PATCH] arm64: kprobes: Drop open-coded exception fixup
Date: Thu, 17 Oct 2019 16:31:42 +0100 [thread overview]
Message-ID: <e70f7b9de7e601b9e4a6fedad8eaf64d304b1637.1571326276.git.robin.murphy@arm.com> (raw)
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:
- 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.
- 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.
- __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.
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
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next reply other threads:[~2019-10-17 15:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-17 15:31 Robin Murphy [this message]
2019-10-21 8:49 ` [PATCH] arm64: kprobes: Drop open-coded exception fixup Masami Hiramatsu
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