linux-kernel - Re: [PATCH 0/2] drm/radeon: have the callers of set_memory

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Date:   Wed, 8 Jan 2020 13:56:47 +0100
From:   Christian König <christian.koenig@....com>
To:     Tianlin Li <tli@...italocean.com>,
        kernel-hardening@...ts.openwall.com, keescook@...omium.org
Cc:     Alex Deucher <alexander.deucher@....com>, David1.Zhou@....com,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] drm/radeon: have the callers of set_memory_*() check
 the return value

Am 07.01.20 um 20:25 schrieb Tianlin Li:
> Right now several architectures allow their set_memory_*() family of
> functions to fail, but callers may not be checking the return values.
> If set_memory_*() returns with an error, call-site assumptions may be
> infact wrong to assume that it would either succeed or not succeed at
> all. Ideally, the failure of set_memory_*() should be passed up the
> call stack, and callers should examine the failure and deal with it.
>
> Need to fix the callers and add the __must_check attribute. They also
> may not provide any level of atomicity, in the sense that the memory
> protections may be left incomplete on failure. This issue likely has a
> few steps on effects architectures:
> 1)Have all callers of set_memory_*() helpers check the return value.
> 2)Add __must_check to all set_memory_*() helpers so that new uses do
> not ignore the return value.
> 3)Add atomicity to the calls so that the memory protections aren't left
> in a partial state.
>
> This series is part of step 1. Make drm/radeon check the return value of
> set_memory_*().

I'm a little hesitate merge that. This hardware is >15 years old and 
nobody of the developers have any system left to test this change on.

Would it be to much of a problem to just add something like: r = 
set_memory_*(); (void)r; /* Intentionally ignored */.

Apart from that certainly a good idea to add __must_check to the functions.

Regards,
Christian.

>
> Tianlin Li (2):
>    drm/radeon: have the callers of set_memory_*() check the return value
>    drm/radeon: change call sites to handle return value properly.
>
>   drivers/gpu/drm/radeon/r100.c        |  3 ++-
>   drivers/gpu/drm/radeon/radeon.h      |  2 +-
>   drivers/gpu/drm/radeon/radeon_gart.c | 22 ++++++++++++++++++----
>   drivers/gpu/drm/radeon/rs400.c       |  3 ++-
>   4 files changed, 23 insertions(+), 7 deletions(-)
>