5.15-stable review patch. If anyone has any objections, please let me know.
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From: Hao Sun sunhao.th@gmail.com
commit 811c363645b33e6e22658634329e95f383dfc705 upstream.
In check_stack_write_fixed_off(), imm value is cast to u32 before being spilled to the stack. Therefore, the sign information is lost, and the range information is incorrect when load from the stack again.
For the following prog: 0: r2 = r10 1: *(u64*)(r2 -40) = -44 2: r0 = *(u64*)(r2 - 40) 3: if r0 s<= 0xa goto +2 4: r0 = 1 5: exit 6: r0 = 0 7: exit
The verifier gives: func#0 @0 0: R1=ctx(off=0,imm=0) R10=fp0 0: (bf) r2 = r10 ; R2_w=fp0 R10=fp0 1: (7a) *(u64 *)(r2 -40) = -44 ; R2_w=fp0 fp-40_w=4294967252 2: (79) r0 = *(u64 *)(r2 -40) ; R0_w=4294967252 R2_w=fp0 fp-40_w=4294967252 3: (c5) if r0 s< 0xa goto pc+2 mark_precise: frame0: last_idx 3 first_idx 0 subseq_idx -1 mark_precise: frame0: regs=r0 stack= before 2: (79) r0 = *(u64 *)(r2 -40) 3: R0_w=4294967252 4: (b7) r0 = 1 ; R0_w=1 5: (95) exit verification time 7971 usec stack depth 40 processed 6 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
So remove the incorrect cast, since imm field is declared as s32, and __mark_reg_known() takes u64, so imm would be correctly sign extended by compiler.
Fixes: ecdf985d7615 ("bpf: track immediate values written to stack by BPF_ST instruction") Cc: stable@vger.kernel.org Signed-off-by: Hao Sun sunhao.th@gmail.com Acked-by: Shung-Hsi Yu shung-hsi.yu@suse.com Acked-by: Eduard Zingerman eddyz87@gmail.com Link: https://lore.kernel.org/r/20231101-fix-check-stack-write-v3-1-f05c2b1473d5@g... Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2885,7 +2885,7 @@ static int check_stack_write_fixed_off(s insn->imm != 0 && env->bpf_capable) { struct bpf_reg_state fake_reg = {};
- __mark_reg_known(&fake_reg, (u32)insn->imm); + __mark_reg_known(&fake_reg, insn->imm); fake_reg.type = SCALAR_VALUE; save_register_state(state, spi, &fake_reg, size); } else if (reg && is_spillable_regtype(reg->type)) {