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authorJohn Fastabend <john.fastabend@gmail.com>2020-05-29 10:28:40 -0700
committerAlexei Starovoitov <ast@kernel.org>2020-05-29 13:34:06 -0700
commit3a71dc366d4aa51a22f385445f2862231d3fda3b (patch)
treef8c671d98346fec4a52967a908b001d154d2b0d5
parent18644cec714aabbab173729192c7594ee57a406b (diff)
bpf: Fix a verifier issue when assigning 32bit reg states to 64bit ones
With the latest trunk llvm (llvm 11), I hit a verifier issue for test_prog subtest test_verif_scale1. The following simplified example illustrate the issue: w9 = 0 /* R9_w=inv0 */ r8 = *(u32 *)(r1 + 80) /* __sk_buff->data_end */ r7 = *(u32 *)(r1 + 76) /* __sk_buff->data */ ...... w2 = w9 /* R2_w=inv0 */ r6 = r7 /* R6_w=pkt(id=0,off=0,r=0,imm=0) */ r6 += r2 /* R6_w=inv(id=0) */ r3 = r6 /* R3_w=inv(id=0) */ r3 += 14 /* R3_w=inv(id=0) */ if r3 > r8 goto end r5 = *(u32 *)(r6 + 0) /* R6_w=inv(id=0) */ <== error here: R6 invalid mem access 'inv' ... end: In real test_verif_scale1 code, "w9 = 0" and "w2 = w9" are in different basic blocks. In the above, after "r6 += r2", r6 becomes a scalar, which eventually caused the memory access error. The correct register state should be a pkt pointer. The inprecise register state starts at "w2 = w9". The 32bit register w9 is 0, in __reg_assign_32_into_64(), the 64bit reg->smax_value is assigned to be U32_MAX. The 64bit reg->smin_value is 0 and the 64bit register itself remains constant based on reg->var_off. In adjust_ptr_min_max_vals(), the verifier checks for a known constant, smin_val must be equal to smax_val. Since they are not equal, the verifier decides r6 is a unknown scalar, which caused later failure. The llvm10 does not have this issue as it generates different code: w9 = 0 /* R9_w=inv0 */ r8 = *(u32 *)(r1 + 80) /* __sk_buff->data_end */ r7 = *(u32 *)(r1 + 76) /* __sk_buff->data */ ...... r6 = r7 /* R6_w=pkt(id=0,off=0,r=0,imm=0) */ r6 += r9 /* R6_w=pkt(id=0,off=0,r=0,imm=0) */ r3 = r6 /* R3_w=pkt(id=0,off=0,r=0,imm=0) */ r3 += 14 /* R3_w=pkt(id=0,off=14,r=0,imm=0) */ if r3 > r8 goto end ... To fix the above issue, we can include zero in the test condition for assigning the s32_max_value and s32_min_value to their 64-bit equivalents smax_value and smin_value. Further, fix the condition to avoid doing zero extension bounds checks when s32_min_value <= 0. This could allow for the case where bounds 32-bit bounds (-1,1) get incorrectly translated to (0,1) 64-bit bounds. When in-fact the -1 min value needs to force U32_MAX bound. Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") Signed-off-by: John Fastabend <john.fastabend@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/159077331983.6014.5758956193749002737.stgit@john-Precision-5820-Tower
-rw-r--r--kernel/bpf/verifier.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index bfea3f9a972f..efe14cf24bc6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1168,14 +1168,14 @@ static void __reg_assign_32_into_64(struct bpf_reg_state *reg)
* but must be positive otherwise set to worse case bounds
* and refine later from tnum.
*/
- if (reg->s32_min_value > 0)
- reg->smin_value = reg->s32_min_value;
- else
- reg->smin_value = 0;
- if (reg->s32_max_value > 0)
+ if (reg->s32_min_value >= 0 && reg->s32_max_value >= 0)
reg->smax_value = reg->s32_max_value;
else
reg->smax_value = U32_MAX;
+ if (reg->s32_min_value >= 0)
+ reg->smin_value = reg->s32_min_value;
+ else
+ reg->smin_value = 0;
}
static void __reg_combine_32_into_64(struct bpf_reg_state *reg)