linux-kernel - Re: [PATCH v2] arm64: armv8_deprecated: Fix undef

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Message-ID: <20200408171741.GB2481@gaia>
Date:   Wed, 8 Apr 2020 18:17:41 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Fredrik Strupe <fredrik@...upe.net>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        will.deacon@....com
Subject: Re: [PATCH v2] arm64: armv8_deprecated: Fix undef_hook mask for
 thumb setend

On Wed, Apr 08, 2020 at 01:29:41PM +0200, Fredrik Strupe wrote:
> For thumb instructions, call_undef_hook() in traps.c first reads a u16,
> and if the u16 indicates a T32 instruction (u16 >= 0xe800), a second
> u16 is read, which then makes up the the lower half-word of a T32
> instruction. For T16 instructions, the second u16 is not read,
> which makes the resulting u32 opcode always have the upper half set to
> 0.
> 
> However, having the upper half of instr_mask in the undef_hook set to 0
> masks out the upper half of all thumb instructions - both T16 and T32.
> This results in trapped T32 instructions with the lower half-word equal
> to the T16 encoding of setend (b650) being matched, even though the upper
> half-word is not 0000 and thus indicates a T32 opcode.
> 
> An example of such a T32 instruction is eaa0b650, which should raise a
> SIGILL since T32 instructions with an eaa prefix are unallocated as per
> Arm ARM, but instead works as a SETEND because the second half-word is set
> to b650.
> 
> This patch fixes the issue by extending instr_mask to include the
> upper u32 half, which will still match T16 instructions where the upper
> half is 0, but not T32 instructions.
> 
> Signed-off-by: Fredrik Strupe <fredrik@...upe.net>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Fixes: 2d888f48e056 ("arm64: Emulate SETEND for AArch32 tasks")

Queued for 5.7. Thanks.

-- 
Catalin