CVE-2025-38279

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

bpf: Do not include stack ptr register in precision backtracking bookkeeping

Yi Lai reported an issue ([1]) where the following warning appears

in kernel dmesg:

[ 60.643604] verifier backtracking bug

[ 60.643635] WARNING: CPU: 10 PID: 2315 at kernel/bpf/verifier.c:4302 __mark_chain_precision+0x3a6c/0x3e10

[ 60.648428] Modules linked in: bpf_testmod(OE)

[ 60.650471] CPU: 10 UID: 0 PID: 2315 Comm: test_progs Tainted: G OE 6.15.0-rc4-gef11287f8289-dirty #327 PREEMPT(full)

[ 60.654385] Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE

[ 60.656682] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014

[ 60.660475] RIP: 0010:__mark_chain_precision+0x3a6c/0x3e10

[ 60.662814] Code: 5a 30 84 89 ea e8 c4 d9 01 00 80 3d 3e 7d d8 04 00 0f 85 60 fa ff ff c6 05 31 7d d8 04

01 48 c7 c7 00 58 30 84 e8 c4 06 a5 ff <0f> 0b e9 46 fa ff ff 48 ...

[ 60.668720] RSP: 0018:ffff888116cc7298 EFLAGS: 00010246

[ 60.671075] RAX: 54d70e82dfd31900 RBX: ffff888115b65e20 RCX: 0000000000000000

[ 60.673659] RDX: 0000000000000001 RSI: 0000000000000004 RDI: 00000000ffffffff

[ 60.676241] RBP: 0000000000000400 R08: ffff8881f6f23bd3 R09: 1ffff1103ede477a

[ 60.678787] R10: dffffc0000000000 R11: ffffed103ede477b R12: ffff888115b60ae8

[ 60.681420] R13: 1ffff11022b6cbc4 R14: 00000000fffffff2 R15: 0000000000000001

[ 60.684030] FS: 00007fc2aedd80c0(0000) GS:ffff88826fa8a000(0000) knlGS:0000000000000000

[ 60.686837] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

[ 60.689027] CR2: 000056325369e000 CR3: 000000011088b002 CR4: 0000000000370ef0

[ 60.691623] Call Trace:

[ 60.692821] <TASK>

[ 60.693960] ? __pfx_verbose+0x10/0x10

[ 60.695656] ? __pfx_disasm_kfunc_name+0x10/0x10

[ 60.697495] check_cond_jmp_op+0x16f7/0x39b0

[ 60.699237] do_check+0x58fa/0xab10

...

Further analysis shows the warning is at line 4302 as below:

4294 /* static subprog call instruction, which

4295 * means that we are exiting current subprog,

4296 * so only r1-r5 could be still requested as

4297 * precise, r0 and r6-r10 or any stack slot in

4298 * the current frame should be zero by now

4299 */

4300 if (bt_reg_mask(bt) & ~BPF_REGMASK_ARGS) {

4301 verbose(env, "BUG regs %x\n", bt_reg_mask(bt));

4302 WARN_ONCE(1, "verifier backtracking bug");

4303 return -EFAULT;

4304 }

With the below test (also in the next patch):

__used __naked static void __bpf_jmp_r10(void)

{

asm volatile (

"r2 = 2314885393468386424 ll;"

"goto +0;"

"if r2 <= r10 goto +3;"

"if r1 >= -1835016 goto +0;"

"if r2 <= 8 goto +0;"

"if r3 <= 0 goto +0;"

"exit;"

::: __clobber_all);

}

SEC("?raw_tp")

__naked void bpf_jmp_r10(void)

{

asm volatile (

"r3 = 0 ll;"

"call __bpf_jmp_r10;"

"r0 = 0;"

"exit;"

::: __clobber_all);

}

The following is the verifier failure log:

0: (18) r3 = 0x0 ; R3_w=0

2: (85) call pc+2

caller:

R10=fp0

callee:

frame1: R1=ctx() R3_w=0 R10=fp0

5: frame1: R1=ctx() R3_w=0 R10=fp0

; asm volatile (" \ @ verifier_precision.c:184

5: (18) r2 = 0x20202000256c6c78 ; frame1: R2_w=0x20202000256c6c78

7: (05) goto pc+0

8: (bd) if r2 <= r10 goto pc+3 ; frame1: R2_w=0x20202000256c6c78 R10=fp0

9: (35) if r1 >= 0xffe3fff8 goto pc+0 ; frame1: R1=ctx()

10: (b5) if r2 <= 0x8 goto pc+0

mark_precise: frame1: last_idx 10 first_idx 0 subseq_idx -1

mark_precise: frame1: regs=r2 stack= before 9: (35) if r1 >= 0xffe3fff8 goto pc+0

mark_precise: frame1: regs=r2 stack= before 8: (bd) if r2 <= r10 goto pc+3

mark_preci

---truncated---