On Tue, Apr 22, 2025 at 10:56 AM Kees Cook <k...@kernel.org> wrote: > > On Tue, Apr 22, 2025 at 09:22:26AM -0400, Alex Deucher wrote: > > On Mon, Apr 21, 2025 at 5:59 PM Kees Cook <k...@kernel.org> wrote: > > > > > > GCC really does not want to consider NULL (or near-NULL) addresses as > > > valid, so calculations based off of NULL end up getting range-tracked into > > > being an offset wthin a 0 byte array. It gets especially mad about this: > > > > > > if (vbios_str == NULL) > > > vbios_str += sizeof(BIOS_ATOM_PREFIX) - 1; > > > ... > > > if (vbios_str != NULL && *vbios_str == 0) > > > vbios_str++; > > > > > > It sees this as being "sizeof(BIOS_ATOM_PREFIX) - 1" byte offset from > > > NULL, when building with -Warray-bounds (and the coming > > > -fdiagnostic-details flag): > > > > > > In function 'atom_get_vbios_pn', > > > inlined from 'amdgpu_atom_parse' at > > > drivers/gpu/drm/amd/amdgpu/atom.c:1553:2: > > > drivers/gpu/drm/amd/amdgpu/atom.c:1447:34: error: array subscript 0 is > > > outside array bounds of 'unsigned char[0]' [-Werror=array-bounds=] > > > 1447 | if (vbios_str != NULL && *vbios_str == 0) > > > | ^~~~~~~~~~ > > > 'amdgpu_atom_parse': events 1-2 > > > 1444 | if (vbios_str == NULL) > > > | ^ > > > | | > > > | (1) when the condition is evaluated to true > > > ...... > > > 1447 | if (vbios_str != NULL && *vbios_str == 0) > > > | ~~~~~~~~~~ > > > | | > > > | (2) out of array bounds here > > > In function 'amdgpu_atom_parse': > > > cc1: note: source object is likely at address zero > > > > > > As there isn't a sane way to convince it otherwise, hide vbios_str from > > > GCC's optimizer to avoid the warning so we can get closer to enabling > > > -Warray-bounds globally. > > > > > > Signed-off-by: Kees Cook <k...@kernel.org> > > > > Acked-by: Alex Deucher <alexander.deuc...@amd.com> > > Thanks! > > > Do you want me to pick this up, or do you want to take this through > > some other tree? > > Whatever is easier for you. I'm happy to carry it if you'd like. :) > There's no rush on these -- it's been a long road to getting > -Warray-bounds enabled. ;)
I've picked it up. Thanks! Alex > > -- > Kees Cook
