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

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Message-ID: <e1561019-21c2-04f9-5db7-1c27c327a8db@virtuozzo.com>
Date:   Thu, 8 Feb 2018 19:05:14 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] UBSAN: support __ubsan_handle_type_mismatch_v1



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 ;)

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