linux-kernel - Re: [PATCH v2] drm/radeon: have the callers of set_memory

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Message-ID: <6e5a18f6-b7f6-c401-c845-fe24b183f348@amd.com>
Date:   Mon, 3 Feb 2020 18:16:33 +0100
From:   Christian König <christian.koenig@....com>
To:     Tianlin Li <tli@...italocean.com>,
        kernel-hardening@...ts.openwall.com
Cc:     keescook@...omium.org, 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 v2] drm/radeon: have the callers of set_memory_*() check
 the return value

Am 03.02.20 um 17:18 schrieb Tianlin Li:
> Right now several architectures allow their set_memory_*() family of
> functions to fail,

Oh, that is a detail I previously didn't recognized. Which architectures 
are that?

Cause the RS400/480, RS690 and RS740 which are affected by this are 
integrated in the south-bridge.

>   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_*().
>
> Signed-off-by: Tianlin Li <tli@...italocean.com>

Reviewed-by: Christian König <christian.koenig@....com>

> ---
> v2:
> The hardware is too old to be tested on and the code cannot be simply
> removed from the kernel, so this is the solution for the short term.
> - Just print an error when something goes wrong
> - Remove patch 2.
> v1:
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F20200107192555.20606-1-tli%40digitalocean.com%2F&amp;data=02%7C01%7Cchristian.koenig%40amd.com%7Cba2176d2ca834214e6b108d7a8c4bb1d%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637163435227030235&amp;sdata=mDhUEi3vmxahjsdrZOr83OEIWNBHefO8lkXST%2FW32CE%3D&amp;reserved=0
> ---
>   drivers/gpu/drm/radeon/radeon_gart.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/radeon_gart.c b/drivers/gpu/drm/radeon/radeon_gart.c
> index f178ba321715..a2cc864aa08d 100644
> --- a/drivers/gpu/drm/radeon/radeon_gart.c
> +++ b/drivers/gpu/drm/radeon/radeon_gart.c
> @@ -80,8 +80,9 @@ int radeon_gart_table_ram_alloc(struct radeon_device *rdev)
>   #ifdef CONFIG_X86
>   	if (rdev->family == CHIP_RS400 || rdev->family == CHIP_RS480 ||
>   	    rdev->family == CHIP_RS690 || rdev->family == CHIP_RS740) {
> -		set_memory_uc((unsigned long)ptr,
> -			      rdev->gart.table_size >> PAGE_SHIFT);
> +		if (set_memory_uc((unsigned long)ptr,
> +			      rdev->gart.table_size >> PAGE_SHIFT))
> +			DRM_ERROR("set_memory_uc failed.\n");
>   	}
>   #endif
>   	rdev->gart.ptr = ptr;
> @@ -106,8 +107,9 @@ void radeon_gart_table_ram_free(struct radeon_device *rdev)
>   #ifdef CONFIG_X86
>   	if (rdev->family == CHIP_RS400 || rdev->family == CHIP_RS480 ||
>   	    rdev->family == CHIP_RS690 || rdev->family == CHIP_RS740) {
> -		set_memory_wb((unsigned long)rdev->gart.ptr,
> -			      rdev->gart.table_size >> PAGE_SHIFT);
> +		if (set_memory_wb((unsigned long)rdev->gart.ptr,
> +			      rdev->gart.table_size >> PAGE_SHIFT))
> +			DRM_ERROR("set_memory_wb failed.\n");
>   	}
>   #endif
>   	pci_free_consistent(rdev->pdev, rdev->gart.table_size,