From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4275D4218B4; Tue, 31 Mar 2026 16:32:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774974768; cv=none; b=M/DkcEtTR7rchUcv/i9fXF6I7S0Ar/78au3VG1WJhzNRcWSzyo1Zhm+bAY0id8w52Tutpfais/zXEsfpLyhw/hfrPnLzZXvBd9ParD4VOoQyXJf+oXx2eR1Hp+omExJH58S53+UFmrq8WuvYceEJdjYpm92ebhW+iQohns2EhPo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774974768; c=relaxed/simple; bh=JCaSCCxLZFgjTHcM0KQlO1PHesIcKYdf86Dna93d02I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Ycdi6KRQ+PwK51mDm9ZdxPzc4I1rzx8GH7M85vrPQQY5KRUO3fWuLnUU2rv1VESYIltwI7cTl7lkI1/edF1+7USFGR2ZSmWYDfGDOgQ05WI/PB9OKFGRkI95M3mYKoc/BwfXHVjXdC+1i92iC2Mti1knbK7ShJiA5IqUQZeBcKY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=wbeW880l; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="wbeW880l" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CEC4BC19423; Tue, 31 Mar 2026 16:32:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1774974768; bh=JCaSCCxLZFgjTHcM0KQlO1PHesIcKYdf86Dna93d02I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wbeW880lqVLdjtvvo1DLWauUFXf+Iqc7+rsK/LXvGcPiitdNJ6FG42XljjS3QknoH +qcq4BxlU5l/MtPQ0FUu6B9vUigbuIKxAuknuDFGj03Dtw2ZZoZojwbU8y4nDwgfWX LVjYJdd3p+UifF7sJrUFJs4DgfTlPciTo4HCtzlI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Yonghong Song , Mykyta Yatsenko , Jenny Guanni Qu , Alexei Starovoitov , Sasha Levin Subject: [PATCH 6.19 019/342] bpf: Fix undefined behavior in interpreter sdiv/smod for INT_MIN Date: Tue, 31 Mar 2026 18:17:32 +0200 Message-ID: <20260331161759.619343083@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260331161758.909578033@linuxfoundation.org> References: <20260331161758.909578033@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jenny Guanni Qu [ 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 Acked-by: Mykyta Yatsenko Signed-off-by: Jenny Guanni Qu Link: https://lore.kernel.org/r/20260311011116.2108005-2-qguanni@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- 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 1b32333d8f8c6..5a56bc2ab900d 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1754,6 +1754,12 @@ 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 @@ -1918,8 +1924,8 @@ 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 @@ -1946,8 +1952,8 @@ 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 @@ -1973,8 +1979,8 @@ 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 @@ -2000,8 +2006,8 @@ 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 -- 2.51.0