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From: Oliver Swede <oli.swede@arm.com>
To: catalin.marinas@arm.com, will@kernel.org
Cc: robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org
Subject: [PATCH v5 02/14] arm64: kprobes: Drop open-coded exception fixup
Date: Mon, 14 Sep 2020 15:17:48 +0000	[thread overview]
Message-ID: <20200914151800.2270-3-oli.swede@arm.com> (raw)
In-Reply-To: <20200914151800.2270-1-oli.swede@arm.com>

From: Robin Murphy <robin.murphy@arm.com>

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>
Signed-off-by: Oliver Swede <oli.swede@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 5290f17a4d80..c54c8252b32f 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -328,13 +328,6 @@ 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;
 }
-- 
2.17.1


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  parent reply	other threads:[~2020-09-14 15:20 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-14 15:17 [PATCH v5 00/14] Optimise and update memcpy, user copy and string routines Oliver Swede
2020-09-14 15:17 ` [PATCH v5 01/14] arm64: Allow passing fault address to fixup handlers Oliver Swede
2020-09-14 15:17 ` Oliver Swede [this message]
2020-09-14 15:17 ` [PATCH v5 03/14] arm64: Import latest version of Cortex Strings' memcmp Oliver Swede
2020-09-14 15:17 ` [PATCH v5 04/14] arm64: Import latest version of Cortex Strings' memmove Oliver Swede
2020-09-14 15:17 ` [PATCH v5 05/14] arm64: Import latest version of Cortex Strings' strcmp Oliver Swede
2020-09-14 15:17 ` [PATCH v5 06/14] arm64: Import latest version of Cortex Strings' strlen Oliver Swede
2020-09-14 15:17 ` [PATCH v5 07/14] arm64: Import latest version of Cortex Strings' strncmp Oliver Swede
2020-09-14 15:17 ` [PATCH v5 08/14] arm64: Import latest optimization of memcpy Oliver Swede
2020-09-14 15:17 ` [PATCH v5 09/14] arm64: Tidy up _asm_extable_faultaddr usage Oliver Swede
2020-09-14 15:17 ` [PATCH v5 10/14] arm64: usercopy: Store the arguments on stack Oliver Swede
2020-09-14 15:17 ` [PATCH v5 11/14] arm64: usercopy: Check for overlapping buffers in fixup Oliver Swede
2020-09-14 15:17 ` [PATCH v5 12/14] arm64: usercopy: Add intermediate fixup routine Oliver Swede
2020-09-14 15:17 ` [PATCH v5 13/14] arm64: usercopy: Add conclusive " Oliver Swede
2020-09-14 15:18 ` [PATCH v5 14/14] arm64: usercopy: Reduce overhead in fixup Oliver Swede
  -- strict thread matches above, loose matches on Subject: below --
2020-09-14 15:09 [PATCH v5 00/14] Optimise and update memcpy, user copy and string routines Oliver Swede
2020-09-14 15:09 ` [PATCH v5 02/14] arm64: kprobes: Drop open-coded exception fixup Oliver Swede

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