bpf: Fix stack slot index in nospec checks

Overview

In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix stack slot index in nospec checks

check_stack_write_fixed_off() computes the byte slot for a fixed-offset stack write as -off - 1, and records each written byte in slot_type[] with (slot - i) % BPF_REG_SIZE.

The Spectre v4 sanitization pre-check uses slot_type[i] instead. For a 4-byte write at fp-8 after the lower half of fp-8 has been zeroed, the pre-check scans bytes 0..3 and sees STACK_ZERO while the actual write updates bytes 7..4. That can leave the second half-slot write without nospec_result even though the bytes being overwritten still require sanitization.

Use the same slot index in the sanitization pre-check that the write path uses when updating slot_type[].

Affected

• Linux >= 0e9280654aa482088ee6ef3deadef331f5ac5fb0 < e62268e695075a481a6c4feeb022c19cf57422a6
• Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < a71eb8f730a91271cf47ce291e785b6b7e54622f
• Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < ca119656baa8f48a56e0c2f3ab63fdd33ca9e307
• Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < 475405593de2b796224c6297aece44f321195919
• Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < f1471aa76d74e0df3b2a90731ca0208f498c670b
• Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < 68b41e68a62299f26cb16af422b5c7d1c69dafd9
• Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < db8f1dcf5950b91886b9df4270bc816370d292c1
• Linux >= 2039f26f3aca5b0e419b98f65dd36481337b86ee < d1d53aa30ab3b5ae89161c9cc840b3f7489ad386
• Linux 872968502114d68c21419cf7eb5ab97717e7b803
• Linux f5893af2704eb763eb982f01d573f5b19f06b623
• Linux 0b27bdf02c400684225ee5ee99970bcbf5082282
• Linux >= 5.10.56 < 5.10.261
• Linux >= 4.19.207 < 4.20
• Linux >= 5.4.146 < 5.5
• Linux >= 5.13.8 < 5.14
• Linux 5.14

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.