Am 18.10.18 um 19:13 schrieb Wenwen Wang: > 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. Well NAK, that doesn't make any sense to me. First of all we don't map VRAM, but rather the ROM which is a read only flash. Writing to the flash is not supported through the BAR as far as I know. Then we check the first two bytes to make sure that the ROM is correctly mapped and not to prevent any malicious attacks. Regards, Christian. > > 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; > } _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
