In radeon_read_bios(), the bios rom is firstly mapped to the IO memory region 'bios' through pci_map_rom(). Then the first two bytes of 'bios' are copied to 'val1' and 'val2' respectively through readb(). After that, 'val1' and 'val2' are checked to see whether they have expected values, i.e., 0x55 and 0xaa, respectively. If yes, the whole data in 'bios' is then copied to 'rdev->bios' through memcpy_fromio(). Obviously, the first two bytes in 'bios' are copied twice. More importantly, no check is enforced on the first two bytes of 'rdev->bios' after memcpy_fromio(). Given that the IO memory region can also be accessed by the device, it is possible that a malicious device can race to modify these two bytes between the two copies and thus after memcpy_fromio(), the first two bytes in 'rdev->bios' can have unexpected values. This can cause undefined behavior of the kernel and introduce potential security risk, if the device can be controlled by attackers. This patch rewrites the first two bytes of 'rdev->bios' after memcpy_fromio() with expected values. Through this way, the above issue can be avoided. Signed-off-by: Wenwen Wang <wang6495@xxxxxxx> --- drivers/gpu/drm/radeon/radeon_bios.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/gpu/drm/radeon/radeon_bios.c b/drivers/gpu/drm/radeon/radeon_bios.c index 04c0ed4..f336719 100644 --- a/drivers/gpu/drm/radeon/radeon_bios.c +++ b/drivers/gpu/drm/radeon/radeon_bios.c @@ -98,6 +98,8 @@ static bool radeon_read_bios(struct radeon_device *rdev) return false; } memcpy_fromio(rdev->bios, bios, size); + rdev->bios[0] = val1; + rdev->bios[1] = val2; pci_unmap_rom(rdev->pdev, bios); return true; } -- 2.7.4 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
