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From: vladimir.murzin@arm•com (Vladimir Murzin)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/2] arm64: fix dump_instr when PAN and UAO are in use
Date: Mon, 13 Jun 2016 13:15:19 +0100	[thread overview]
Message-ID: <575EA3D7.8040001@arm.com> (raw)
In-Reply-To: <1465812915-19801-2-git-send-email-mark.rutland@arm.com>

On 13/06/16 11:15, Mark Rutland wrote:
> If the kernel is set to show unhandled signals, and a user task does not
> handle a SIGILL as a result of an instruction abort, we will attempt to
> log the offending instruction with dump_instr before killing the task.
> 
> We use dump_instr to log the encoding of the offending userspace
> instruction. However, dump_instr is also used to dump instructions from
> kernel space, and internally always switches to KERNEL_DS before dumping
> the instruction with get_user. When both PAN and UAO are in use, reading
> a user instruction via get_user while in KERNEL_DS will result in a
> permission fault, which leads to an Oops.
> 
> As we have regs corresponding to the context of the original instruction
> abort, we can inspect this and only flip to KERNEL_DS if the original
> abort was taken from the kernel, avoiding this issue. At the same time,
> remove the redundant (and incorrect) comments regarding the order
> dump_mem and dump_instr are called in.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm•com>
> Reported-by: Vladimir Murzin <vladimir.murzin@arm•com>
> Cc: Catalin Marinas <catalin.marinas@arm•com>
> Cc: James Morse <james.morse@arm•com>
> Cc: Robin Murphy <robin.murphy@arm•com>
> Cc: Will Deacon <will.deacon@arm•com>
> Fixes: 57f4959bad0a154a ("arm64: kernel: Add support for User Access Override")

FWIW:

Tested-by: Vladimir Murzin <vladimir.murzin@arm•com>

with

$ echo 0 > /proc/sys/abi/swp

Removed swp emulation handler

$. /swp_test

$ cat swp_test.c

int main(void)
{
        unsigned long ret, x = 42, y = 24;

        asm volatile("swp     %0, %1, [%2]"
                     : "=&r" (ret)
                     : "r" (x), "r" (&y)
                     : "memory");

        return ret;
}

Thanks
Vladimir

next prev parent reply	other threads:[~2016-06-13 12:15 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-13 10:15 [PATCH 0/2] arm64: traps.c fix + cleanup Mark Rutland
2016-06-13 10:15 ` [PATCH 1/2] arm64: fix dump_instr when PAN and UAO are in use Mark Rutland
2016-06-13 12:15   ` Vladimir Murzin [this message]
2016-06-13 12:48   ` Will Deacon
2016-06-13 12:54     ` Mark Rutland
2016-06-13 10:15 ` [PATCH 2/2] arm64: simplify dump_mem Mark Rutland
2016-06-21 14:48   ` Catalin Marinas

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