[PATCH v4 0/2] bpf: Fix abs(INT_MIN) undefined behavior in interpreter sdiv/smod

[Jenny Guanni Qu <qguanni@gmail.com>]

The BPF interpreter's signed 32-bit division and modulo handlers use
abs() on s32 operands, which is undefined for S32_MIN. This causes
the interpreter to compute wrong results, creating a mismatch with
the verifier's range tracking.

For example, INT_MIN / 2 returns 0x40000000 instead of the correct
0xC0000000. The verifier tracks the correct range, so a crafted BPF
program can exploit the mismatch for out-of-bounds map value access
(confirmed by KASAN).

Patch 1 introduces __safe_abs32() which handles S32_MIN correctly
and replaces all 8 abs((s32)...) call sites.

Patch 2 adds selftests covering sdiv32 and smod32 with INT_MIN
dividend to prevent regression.

Changes since v3:
  - Fixed stray blank line deletion in the file header
  - Improved __safe_abs32() comment per Yonghong Song's suggestion
  - Added JIT vs interpreter context to selftest commit message
    per Yonghong Song's feedback

Changes since v2:
  - Simplified __safe_abs32() to use -(u32)x instead of special-casing
    S32_MIN, per Mykyta Yatsenko's suggestion

Changes since v1:
  - Moved __safe_abs32() helper above the kerneldoc comment block
    for ___bpf_prog_run() to fix build warnings reported by
    kernel test robot

Jenny Guanni Qu (2):
  bpf: Fix undefined behavior in interpreter sdiv/smod for INT_MIN
  selftests/bpf: Add tests for sdiv32/smod32 with INT_MIN dividend

 kernel/bpf/core.c                             | 22 ++++---
 .../selftests/bpf/progs/verifier_sdiv.c       | 58 +++++++++++++++++++
 2 files changed, 72 insertions(+), 8 deletions(-)

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2.34.1