linux-kernel - Re: [PATCH] UBSAN: support __ubsan_handle_type_mismatch

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Message-ID: <20180208161645.lol4xqw677yrz5on@lakrids.cambridge.arm.com>
Date:   Thu, 8 Feb 2018 16:16:46 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] UBSAN: support __ubsan_handle_type_mismatch_v1

On Thu, Feb 08, 2018 at 07:05:14PM +0300, Andrey Ryabinin wrote:
> On 02/08/2018 06:46 PM, Mark Rutland wrote:
> > Originally, UBSAN's __ubsan_handle_type_mismatch took a struct
> > type_mismatch_data, as defined in lib/ubsan.h. This has an unsigned long
> > alignment field.
> > 
> > New versions of UBSAN call __ubsan_handle_type_mismatch_v1, which is
> > similar to __ubsan_handle_type_mismatch, but takes a different struct
> > where the alignment is stored in an unsigned char (as log2 of the
> > alignment). All other fields are unchanged.
> > 
> > As we don't implement __ubsan_handle_type_mismatch_v1, the kernel will
> > fail to link when compiled with compilers using the new ABI (e.g. clang
> > form the LLVM 5.0.0 release).
> > 
> > This patch adds support for the new ABI. To keep things simple, we
> > simply convert the new data format into the old format, and hand it on
> > to the existing handlers.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> > ---
> >  lib/ubsan.c | 14 ++++++++++++++
> >  lib/ubsan.h |  7 +++++++
> >  2 files changed, 21 insertions(+)
> > 
> > Andrey, does this look correct to you?
> 
> Almost.
> Commit 42440c1f9911b4b7b8ba3dc4e90c1197bc561211 looks correct to me ;)

Ah, I didn't spot something had already been queued. Sorry for the
noise, and thanks for implementing this!

> Copying ->location is wrong, because we use bit in location struct to suppress multiple
> reports of the same location, see was_reported(). So in you case REPORTED_BIT will be set
> on stack and original source_location remain unchanged.
>
> > Are there any other new ABI bits that need to be plumbed in?
> 
> ABI of __ubsan_handle_nonnull_return() changed as well, but it's never used in the kernel
> and probably never will be. Thus I removed it, see bac7a1fff7926fb9891a18fe33650884b0e13e4

Noted.

I'll cherry-pick these into my local testing branch while I await
v4.16-rc1.

Mark.