In the Linux kernel, the following vulnerability has been resolved:bpf: sync_linked_regs() must preserve subreg_defRange propagation must not affect subreg_def marks, otherwise thefollowing example is rewritten by verifier incorrectly whenBPF_F_TEST_RND_HI32 flag is set: 0: call bpf_ktime_get_ns call bpf_ktime_get_ns 1: r0 &= 0x7fffffff after verifier r0 &= 0x7fffffff 2: w1 = w0 rewrites w1 = w0 3: if w0 < 10 goto +0 --------------> r11 = 0x2f5674a6 (r) 4: r1 >>= 32 r11 <<= 32 (r) 5: r0 = r1 r1 |= r11 (r) 6: exit; if w0 < 0xa goto pc+0 r1 >>= 32 r0 = r1 exit(or zero extension of w1 at (2) is missing for architectures that require zero extension for upper register half).The following happens w/o this patch:- r0 is marked as not a subreg at (0);- w1 is marked as subreg at (2);- w1 subreg_def is overridden at (3) by copy_register_state();- w1 is read at (5) but mark_insn_zext() does not mark (2) for zero extension, because w1 subreg_def is not set;- because of BPF_F_TEST_RND_HI32 flag verifier inserts random value for hi32 bits of (2) (marked (r));- this random value is read at (5). CREATE(Triage):(User=admin) CVE-2024-53125 (https://nvd.nist.gov/vuln/detail/CVE-2024-53125)
