From: Jenny Guanni Qu <qguanni@gmail.com> stable inclusion from stable-v6.6.131 commit 694ea55f1b1c74f9942d91ec366ae9e822422e42 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/14258 CVE: CVE-2026-31525 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit c77b30bd1dcb61f66c640ff7d2757816210c7cb0 ] The BPF interpreter's signed 32-bit division and modulo handlers use the kernel abs() macro on s32 operands. The abs() macro documentation (include/linux/math.h) explicitly states the result is undefined when the input is the type minimum. When DST contains S32_MIN (0x80000000), abs((s32)DST) triggers undefined behavior and returns S32_MIN unchanged on arm64/x86. This value is then sign-extended to u64 as 0xFFFFFFFF80000000, causing do_div() to compute the wrong result. The verifier's abstract interpretation (scalar32_min_max_sdiv) computes the mathematically correct result for range tracking, creating a verifier/interpreter mismatch that can be exploited for out-of-bounds map value access. Introduce abs_s32() which handles S32_MIN correctly by casting to u32 before negating, avoiding signed overflow entirely. Replace all 8 abs((s32)...) call sites in the interpreter's sdiv32/smod32 handlers. s32 is the only affected case -- the s64 division/modulo handlers do not use abs(). Fixes: ec0e2da95f72 ("bpf: Support new signed div/mod instructions.") Acked-by: Yonghong Song <yonghong.song@linux.dev> Acked-by: Mykyta Yatsenko <yatsenko@meta.com> Signed-off-by: Jenny Guanni Qu <qguanni@gmail.com> Link: https://lore.kernel.org/r/20260311011116.2108005-2-qguanni@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Pu Lehui <pulehui@huawei.com> --- kernel/bpf/core.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 72a7503a59d0..e9ca3e36783e 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1668,6 +1668,12 @@ bool bpf_opcode_in_insntable(u8 code) } #ifndef CONFIG_BPF_JIT_ALWAYS_ON +/* Absolute value of s32 without undefined behavior for S32_MIN */ +static u32 abs_s32(s32 x) +{ + return x >= 0 ? (u32)x : -(u32)x; +} + /** * ___bpf_prog_run - run eBPF program on a given context * @regs: is the array of MAX_BPF_EXT_REG eBPF pseudo-registers @@ -1832,8 +1838,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) DST = do_div(AX, (u32) SRC); break; case 1: - AX = abs((s32)DST); - AX = do_div(AX, abs((s32)SRC)); + AX = abs_s32((s32)DST); + AX = do_div(AX, abs_s32((s32)SRC)); if ((s32)DST < 0) DST = (u32)-AX; else @@ -1860,8 +1866,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) DST = do_div(AX, (u32) IMM); break; case 1: - AX = abs((s32)DST); - AX = do_div(AX, abs((s32)IMM)); + AX = abs_s32((s32)DST); + AX = do_div(AX, abs_s32((s32)IMM)); if ((s32)DST < 0) DST = (u32)-AX; else @@ -1887,8 +1893,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) DST = (u32) AX; break; case 1: - AX = abs((s32)DST); - do_div(AX, abs((s32)SRC)); + AX = abs_s32((s32)DST); + do_div(AX, abs_s32((s32)SRC)); if (((s32)DST < 0) == ((s32)SRC < 0)) DST = (u32)AX; else @@ -1914,8 +1920,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) DST = (u32) AX; break; case 1: - AX = abs((s32)DST); - do_div(AX, abs((s32)IMM)); + AX = abs_s32((s32)DST); + do_div(AX, abs_s32((s32)IMM)); if (((s32)DST < 0) == ((s32)IMM < 0)) DST = (u32)AX; else -- 2.34.1