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authorIlya Leoshkevich <iii@linux.ibm.com>2019-07-19 11:18:15 +0200
committerAlexei Starovoitov <ast@kernel.org>2019-07-23 13:59:33 -0700
commitd9b8aadaffa65809d146cf0f8632a22a946367d7 (patch)
tree21a5bdbf346e257044943c096bde20c522b7e70a
parentc8eee4135a456bc031d67cadc454e76880d1afd8 (diff)
bpf: fix narrower loads on s390
The very first check in test_pkt_md_access is failing on s390, which happens because loading a part of a struct __sk_buff field produces an incorrect result. The preprocessed code of the check is: { __u8 tmp = *((volatile __u8 *)&skb->len + ((sizeof(skb->len) - sizeof(__u8)) / sizeof(__u8))); if (tmp != ((*(volatile __u32 *)&skb->len) & 0xFF)) return 2; }; clang generates the following code for it: 0: 71 21 00 03 00 00 00 00 r2 = *(u8 *)(r1 + 3) 1: 61 31 00 00 00 00 00 00 r3 = *(u32 *)(r1 + 0) 2: 57 30 00 00 00 00 00 ff r3 &= 255 3: 5d 23 00 1d 00 00 00 00 if r2 != r3 goto +29 <LBB0_10> Finally, verifier transforms it to: 0: (61) r2 = *(u32 *)(r1 +104) 1: (bc) w2 = w2 2: (74) w2 >>= 24 3: (bc) w2 = w2 4: (54) w2 &= 255 5: (bc) w2 = w2 The problem is that when verifier emits the code to replace a partial load of a struct __sk_buff field (*(u8 *)(r1 + 3)) with a full load of struct sk_buff field (*(u32 *)(r1 + 104)), an optional shift and a bitwise AND, it assumes that the machine is little endian and incorrectly decides to use a shift. Adjust shift count calculation to account for endianness. Fixes: 31fd85816dbe ("bpf: permits narrower load from bpf program context fields") Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
-rw-r--r--include/linux/filter.h13
-rw-r--r--kernel/bpf/verifier.c4
2 files changed, 15 insertions, 2 deletions
diff --git a/include/linux/filter.h b/include/linux/filter.h
index ff65d22cf336..92c6e31fb008 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -24,6 +24,7 @@
#include <net/sch_generic.h>
+#include <asm/byteorder.h>
#include <uapi/linux/filter.h>
#include <uapi/linux/bpf.h>
@@ -747,6 +748,18 @@ bpf_ctx_narrow_access_ok(u32 off, u32 size, u32 size_default)
return size <= size_default && (size & (size - 1)) == 0;
}
+static inline u8
+bpf_ctx_narrow_load_shift(u32 off, u32 size, u32 size_default)
+{
+ u8 load_off = off & (size_default - 1);
+
+#ifdef __LITTLE_ENDIAN
+ return load_off * 8;
+#else
+ return (size_default - (load_off + size)) * 8;
+#endif
+}
+
#define bpf_ctx_wide_access_ok(off, size, type, field) \
(size == sizeof(__u64) && \
off >= offsetof(type, field) && \
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5900cbb966b1..c84d83f86141 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8616,8 +8616,8 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
}
if (is_narrower_load && size < target_size) {
- u8 shift = (off & (size_default - 1)) * 8;
-
+ u8 shift = bpf_ctx_narrow_load_shift(off, size,
+ size_default);
if (ctx_field_size <= 4) {
if (shift)
insn_buf[cnt++] = BPF_ALU32_IMM(BPF_RSH,