linux-kernel - Re: [PING] [PATCH v2] arm: ptrace: Fix mask for thumb breakpoint hook

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Message-ID: <20200518163940.GW1551@shell.armlinux.org.uk>
Date:   Mon, 18 May 2020 17:39:40 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Fredrik Strupe <fredrik@...upe.net>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PING] [PATCH v2] arm: ptrace: Fix mask for thumb breakpoint hook

On Mon, May 18, 2020 at 05:02:27PM +0200, Fredrik Strupe wrote:
> On 18.05.2020 16:18, Russell King - ARM Linux admin wrote:
> > On Mon, May 18, 2020 at 03:12:06PM +0200, Fredrik Strupe wrote:
> >> call_undef_hook() in traps.c applies the same instr_mask for both 16-bit
> >> and 32-bit thumb instructions. If instr_mask then is only 16 bits wide
> >> (0xffff as opposed to 0xffffffff), the first half-word of 32-bit thumb
> >> instructions will be masked out. This makes the function match 32-bit
> >> thumb instructions where the second half-word is equal to instr_val,
> >> regardless of the first half-word.
> >>
> >> The result in this case is that all undefined 32-bit thumb instructions
> >> with the second half-word equal to de01 (udf #1) work as breakpoints
> >> and will raise a SIGTRAP instead of a SIGILL, instead of just the one
> >> intended 16-bit instruction. An example of such an instruction is
> >> eaa0b650, which is unallocated according to Arm ARM and should raise a
> >> SIGILL, but instead raises a SIGTRAP.
> >
> > How can 0xeaa0b650 match 0xde01 when masked with 0xffff ?
> >
> 
> Sorry, that is a typo; it should say 0xeaa0de01.
> 
> For reference, this is similar to the problem with SETEND emulation that
> was fixed in commit fc2266011acc in the mainline kernel
> (or as discussed here: https://lkml.org/lkml/2020/4/8/274).

Thanks for the clarification.  Please update the patch description and
put it in the patch system, thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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