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author | Luke Nelson <lukenels@cs.washington.edu> | 2020-04-22 20:36:29 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-05-02 18:25:53 +0300 |
commit | 8e28b8489d7f6330544706abf43bd0d152781c88 (patch) | |
tree | 808020bb8362d1d27cf0619334d359f9c7ce041b /arch/x86/net | |
parent | 5f8370cdc6ad4f8a8adeb9cc52ccd48c709d3c03 (diff) | |
download | linux-8e28b8489d7f6330544706abf43bd0d152781c88.tar.xz |
bpf, x86_32: Fix incorrect encoding in BPF_LDX zero-extension
commit 5fa9a98fb10380e48a398998cd36a85e4ef711d6 upstream.
The current JIT uses the following sequence to zero-extend into the
upper 32 bits of the destination register for BPF_LDX BPF_{B,H,W},
when the destination register is not on the stack:
EMIT3(0xC7, add_1reg(0xC0, dst_hi), 0);
The problem is that C7 /0 encodes a MOV instruction that requires a 4-byte
immediate; the current code emits only 1 byte of the immediate. This
means that the first 3 bytes of the next instruction will be treated as
the rest of the immediate, breaking the stream of instructions.
This patch fixes the problem by instead emitting "xor dst_hi,dst_hi"
to clear the upper 32 bits. This fixes the problem and is more efficient
than using MOV to load a zero immediate.
This bug may not be currently triggerable as BPF_REG_AX is the only
register not stored on the stack and the verifier uses it in a limited
way, and the verifier implements a zero-extension optimization. But the
JIT should avoid emitting incorrect encodings regardless.
Fixes: 03f5781be2c7b ("bpf, x86_32: add eBPF JIT compiler for ia32")
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Acked-by: Wang YanQing <udknight@gmail.com>
Link: https://lore.kernel.org/bpf/20200422173630.8351-1-luke.r.nels@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/x86/net')
-rw-r--r-- | arch/x86/net/bpf_jit_comp32.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c index 24d573bc550d..21df0b6d7be6 100644 --- a/arch/x86/net/bpf_jit_comp32.c +++ b/arch/x86/net/bpf_jit_comp32.c @@ -1830,7 +1830,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, STACK_VAR(dst_hi)); EMIT(0x0, 4); } else { - EMIT3(0xC7, add_1reg(0xC0, dst_hi), 0); + /* xor dst_hi,dst_hi */ + EMIT2(0x33, + add_2reg(0xC0, dst_hi, dst_hi)); } break; case BPF_DW: |