[PATCH 5.15 562/917] bpf: Fix propagation of bounds from 64-bit min/max into 32-bit and var_off.

Greg Kroah-Hartman
2021-11-15T23:49:55Z

From: Alexei Starovoitov <ast@kernel.org>

[ Upstream commit b9979db8340154526d9ab38a1883d6f6ba9b6d47 ]

Before this fix:
166: (b5) if r2 <= 0x1 goto pc+22
from 166 to 189: R2=invP(id=1,umax_value=1,var_off=(0x0; 0xffffffff))

After this fix:
166: (b5) if r2 <= 0x1 goto pc+22
from 166 to 189: R2=invP(id=1,umax_value=1,var_off=(0x0; 0x1))

While processing BPF_JLE the reg_set_min_max() would set true_reg->umax_value = 1
and call __reg_combine_64_into_32(true_reg).

Without the fix it would not pass the condition:
if (__reg64_bound_u32(reg->umin_value) && __reg64_bound_u32(reg->umax_value))

since umin_value == 0 at this point.
Before commit 10bf4e83167c the umin was incorrectly ingored.
The commit 10bf4e83167c fixed the correctness issue, but pessimized
propagation of 64-bit min max into 32-bit min max and corresponding var_off.

Fixes: 10bf4e83167c ("bpf: Fix propagation of 32 bit unsigned bounds from 64 bit bounds")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20211101222153.78759-1-alexei.starovoitov@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/verifier.c | 2 +-
tools/testing/selftests/bpf/verifier/array_access.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e76b559179054..055012faca94e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1411,7 +1411,7 @@ static bool __reg64_bound_s32(s64 a)

static bool __reg64_bound_u32(u64 a)
{
- return a > U32_MIN && a < U32_MAX;
+ return a >= U32_MIN && a <= U32_MAX;
}

static void __reg_combine_64_into_32(struct bpf_reg_state *reg)
diff --git a/tools/testing/selftests/bpf/verifier/array_access.c b/tools/testing/selftests/bpf/verifier/array_access.c
index 1b1c798e92489..1b138cd2b187d 100644
--- a/tools/testing/selftests/bpf/verifier/array_access.c
+++ b/tools/testing/selftests/bpf/verifier/array_access.c
@@ -186,7 +186,7 @@
},
.fixup_map_hash_48b = { 3 },
.errstr_unpriv = "R0 leaks addr",
- .errstr = "R0 unbounded memory access",
+ .errstr = "invalid access to map value, value_size=48 off=44 size=8",
.result_unpriv = REJECT,
.result = REJECT,
.flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,
--
2.33.0