On January 22, 2024 8:00:26 PM PST, Yonghong Song <yonghong.song@xxxxxxxxx> wrote: > >On 1/22/24 4:27 PM, Kees Cook wrote: >> In an effort to separate intentional arithmetic wrap-around from >> unexpected wrap-around, we need to refactor places that depend on this >> kind of math. One of the most common code patterns of this is: >> >> VAR + value < VAR >> >> Notably, this is considered "undefined behavior" for signed and pointer >> types, which the kernel works around by using the -fno-strict-overflow >> option in the build[1] (which used to just be -fwrapv). Regardless, we >> want to get the kernel source to the position where we can meaningfully >> instrument arithmetic wrap-around conditions and catch them when they >> are unexpected, regardless of whether they are signed[2], unsigned[3], >> or pointer[4] types. >> >> Refactor open-coded wrap-around addition test to use add_would_overflow(). >> This paves the way to enabling the wrap-around sanitizers in the future. >> >> Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] >> Link: https://github.com/KSPP/linux/issues/26 [2] >> Link: https://github.com/KSPP/linux/issues/27 [3] >> Link: https://github.com/KSPP/linux/issues/344 [4] >> Cc: Alexei Starovoitov <ast@xxxxxxxxxx> >> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> >> Cc: John Fastabend <john.fastabend@xxxxxxxxx> >> Cc: Andrii Nakryiko <andrii@xxxxxxxxxx> >> Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx> >> Cc: Song Liu <song@xxxxxxxxxx> >> Cc: Yonghong Song <yonghong.song@xxxxxxxxx> >> Cc: KP Singh <kpsingh@xxxxxxxxxx> >> Cc: Stanislav Fomichev <sdf@xxxxxxxxxx> >> Cc: Hao Luo <haoluo@xxxxxxxxxx> >> Cc: Jiri Olsa <jolsa@xxxxxxxxxx> >> Cc: bpf@xxxxxxxxxxxxxxx >> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> >> --- >> kernel/bpf/verifier.c | 12 ++++++------ >> 1 file changed, 6 insertions(+), 6 deletions(-) >> >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >> index 65f598694d55..21e3f30c8757 100644 >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c >> @@ -12901,8 +12901,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, >> dst_reg->smin_value = smin_ptr + smin_val; >> dst_reg->smax_value = smax_ptr + smax_val; >> } >> - if (umin_ptr + umin_val < umin_ptr || >> - umax_ptr + umax_val < umax_ptr) { >> + if (add_would_overflow(umin_ptr, umin_val) || >> + add_would_overflow(umax_ptr, umax_val)) { > >Maybe you could give a reference to the definition of add_would_overflow()? >A link or a patch with add_would_overflow() defined cc'ed to bpf program. Sure! It was earlier in the series: https://lore.kernel.org/linux-hardening/20240123002814.1396804-2-keescook@xxxxxxxxxxxx/ The cover letter also has more details: https://lore.kernel.org/linux-hardening/20240122235208.work.748-kees@xxxxxxxxxx/ >The patch itselfs looks good to me. Thanks! -Kees -- Kees Cook
