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

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Date:   Mon,  3 Feb 2020 10:18:27 -0600
From:   Tianlin Li <tli@...italocean.com>
To:     kernel-hardening@...ts.openwall.com
Cc:     keescook@...omium.org, Alex Deucher <alexander.deucher@....com>,
        christian.koenig@....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,
        Tianlin Li <tli@...italocean.com>
Subject: [PATCH v2] drm/radeon: have the callers of set_memory_*() check the return value

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_*().

Signed-off-by: Tianlin Li <tli@...italocean.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://lore.kernel.org/lkml/20200107192555.20606-1-tli@digitalocean.com/
---
 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,
-- 
2.17.1