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| author | Daniel Borkmann <daniel@iogearbox.net> | 2017-06-07 13:45:37 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-06-07 15:27:20 -0400 |
| commit | 7005cade1bdbb423413f8aafcbf17a1ec614a585 (patch) | |
| tree | 77db17f9c82e93e483ff877ae2df8ef0fed79bcc | |
| parent | e173db36e3090d90651d97ab4bc45ace7f8cc0c6 (diff) | |
| download | linux-7005cade1bdbb423413f8aafcbf17a1ec614a585.tar.bz2 | |
bpf, arm64: use separate register for state in stxr
Will reported that in BPF_XADD we must use a different register in stxr
instruction for the status flag due to otherwise CONSTRAINED UNPREDICTABLE
behavior per architecture. Reference manual says [1]:
If s == t, then one of the following behaviors must occur:
* The instruction is UNDEFINED.
* The instruction executes as a NOP.
* The instruction performs the store to the specified address, but
the value stored is UNKNOWN.
Thus, use a different temporary register for the status flag to fix it.
Disassembly extract from test 226/STX_XADD_DW from test_bpf.ko:
[...]
0000003c: c85f7d4b ldxr x11, [x10]
00000040: 8b07016b add x11, x11, x7
00000044: c80c7d4b stxr w12, x11, [x10]
00000048: 35ffffac cbnz w12, 0x0000003c
[...]
[1] https://static.docs.arm.com/ddi0487/b/DDI0487B_a_armv8_arm.pdf, p.6132
Fixes: 85f68fe89832 ("bpf, arm64: implement jiting of BPF_XADD")
Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | arch/arm64/net/bpf_jit_comp.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index 71f930501ade..c870d6f01ac2 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -36,6 +36,7 @@ int bpf_jit_enable __read_mostly; #define TMP_REG_1 (MAX_BPF_JIT_REG + 0) #define TMP_REG_2 (MAX_BPF_JIT_REG + 1) #define TCALL_CNT (MAX_BPF_JIT_REG + 2) +#define TMP_REG_3 (MAX_BPF_JIT_REG + 3) /* Map BPF registers to A64 registers */ static const int bpf2a64[] = { @@ -57,6 +58,7 @@ static const int bpf2a64[] = { /* temporary registers for internal BPF JIT */ [TMP_REG_1] = A64_R(10), [TMP_REG_2] = A64_R(11), + [TMP_REG_3] = A64_R(12), /* tail_call_cnt */ [TCALL_CNT] = A64_R(26), /* temporary register for blinding constants */ @@ -319,6 +321,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx) const u8 src = bpf2a64[insn->src_reg]; const u8 tmp = bpf2a64[TMP_REG_1]; const u8 tmp2 = bpf2a64[TMP_REG_2]; + const u8 tmp3 = bpf2a64[TMP_REG_3]; const s16 off = insn->off; const s32 imm = insn->imm; const int i = insn - ctx->prog->insnsi; @@ -689,10 +692,10 @@ emit_cond_jmp: emit(A64_PRFM(tmp, PST, L1, STRM), ctx); emit(A64_LDXR(isdw, tmp2, tmp), ctx); emit(A64_ADD(isdw, tmp2, tmp2, src), ctx); - emit(A64_STXR(isdw, tmp2, tmp, tmp2), ctx); + emit(A64_STXR(isdw, tmp2, tmp, tmp3), ctx); jmp_offset = -3; check_imm19(jmp_offset); - emit(A64_CBNZ(0, tmp2, jmp_offset), ctx); + emit(A64_CBNZ(0, tmp3, jmp_offset), ctx); break; /* R0 = ntohx(*(size *)(((struct sk_buff *)R6)->data + imm)) */ |