From: Linus Torvalds torvalds@linux-foundation.org
commit fec4d42724a1bf3dcba52307e55375fdb967b852 upstream.
intel_dp_check_mst_status() uses a 14-byte array to read the DPRX Event Status Indicator data, but then passes that buffer at offset 10 off as an argument to drm_dp_channel_eq_ok().
End result: there are only 4 bytes remaining of the buffer, yet drm_dp_channel_eq_ok() wants a 6-byte buffer. gcc-11 correctly warns about this case:
drivers/gpu/drm/i915/display/intel_dp.c: In function ‘intel_dp_check_mst_status’: drivers/gpu/drm/i915/display/intel_dp.c:3491:22: warning: ‘drm_dp_channel_eq_ok’ reading 6 bytes from a region of size 4 [-Wstringop-overread] 3491 | !drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) { | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ drivers/gpu/drm/i915/display/intel_dp.c:3491:22: note: referencing argument 1 of type ‘const u8 *’ {aka ‘const unsigned char *’} In file included from drivers/gpu/drm/i915/display/intel_dp.c:38: include/drm/drm_dp_helper.h:1466:6: note: in a call to function ‘drm_dp_channel_eq_ok’ 1466 | bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE], | ^~~~~~~~~~~~~~~~~~~~ 6:14 elapsed
This commit just extends the original array by 2 zero-initialized bytes, avoiding the warning.
There may be some underlying bug in here that caused this confusion, but this is at least no worse than the existing situation that could use random data off the stack.
Cc: Jani Nikula jani.nikula@intel.com Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Dave Airlie airlied@redhat.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/i915/display/intel_dp.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
--- a/drivers/gpu/drm/i915/display/intel_dp.c +++ b/drivers/gpu/drm/i915/display/intel_dp.c @@ -4488,7 +4488,18 @@ intel_dp_check_mst_status(struct intel_d drm_WARN_ON_ONCE(&i915->drm, intel_dp->active_mst_links < 0);
for (;;) { - u8 esi[DP_DPRX_ESI_LEN] = {}; + /* + * The +2 is because DP_DPRX_ESI_LEN is 14, but we then + * pass in "esi+10" to drm_dp_channel_eq_ok(), which + * takes a 6-byte array. So we actually need 16 bytes + * here. + * + * Somebody who knows what the limits actually are + * should check this, but for now this is at least + * harmless and avoids a valid compiler warning about + * using more of the array than we have allocated. + */ + u8 esi[DP_DPRX_ESI_LEN+2] = {}; bool handled; int retry;