diff mbox series

[bpf,v3,1/2] bpf: Fix check_stack_write_fixed_off() to correctly spill imm

Message ID 20231101-fix-check-stack-write-v3-1-f05c2b1473d5@gmail.com (mailing list archive)
State Accepted
Commit 811c363645b33e6e22658634329e95f383dfc705
Delegated to: BPF
Headers show
Series bpf: Fix incorrect immediate spill | expand

Checks

Context Check Description
bpf/vmtest-bpf-VM_Test-6 success Logs for aarch64-gcc / test (test_progs_no_alu32, false, 360) / test_progs_no_alu32 on aarch64 with gcc
bpf/vmtest-bpf-VM_Test-7 success Logs for aarch64-gcc / test (test_verifier, false, 360) / test_verifier on aarch64 with gcc
bpf/vmtest-bpf-VM_Test-8 success Logs for aarch64-gcc / veristat
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf
netdev/fixes_present success Fixes tag present in non-next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1374 this patch: 1374
netdev/cc_maintainers success CCed 13 of 13 maintainers
netdev/build_clang success Errors and warnings before: 1387 this patch: 1387
netdev/verify_signedoff success Signed-off-by tag matches author and committer
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netdev/verify_fixes success Fixes tag looks correct
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bpf/vmtest-bpf-VM_Test-19 success Logs for x86_64-gcc / test (test_progs_no_alu32, false, 360) / test_progs_no_alu32 on x86_64 with gcc
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bpf/vmtest-bpf-VM_Test-27 success Logs for x86_64-llvm-16 / test (test_progs_no_alu32, false, 360) / test_progs_no_alu32 on x86_64 with llvm-16
bpf/vmtest-bpf-VM_Test-28 success Logs for x86_64-llvm-16 / test (test_verifier, false, 360) / test_verifier on x86_64 with llvm-16
bpf/vmtest-bpf-VM_Test-29 success Logs for x86_64-llvm-16 / veristat
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Commit Message

Hao Sun Nov. 1, 2023, 12:33 p.m. UTC 
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>
---
 kernel/bpf/verifier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 857d76694517..44af69ce1301 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4674,7 +4674,7 @@  static int check_stack_write_fixed_off(struct bpf_verifier_env *env,
 		   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)) {