Commit c77b30bd1dcb for kernel

commit c77b30bd1dcb61f66c640ff7d2757816210c7cb0
Author: Jenny Guanni Qu <qguanni@gmail.com>
Date:   Wed Mar 11 01:11:15 2026 +0000

    bpf: Fix undefined behavior in interpreter sdiv/smod for INT_MIN

    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>

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 9e126be33755..7b675a451ec8 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1757,6 +1757,12 @@ 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
@@ -1921,8 +1927,8 @@ 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
@@ -1949,8 +1955,8 @@ 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
@@ -1976,8 +1982,8 @@ 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
@@ -2003,8 +2009,8 @@ 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