From f4483f2cc1fdc03488c8a1452e545545ae5bda93 Mon Sep 17 00:00:00 2001 From: Russell King Date: Sat, 13 Jan 2018 11:39:54 +0000 Subject: ARM: net: bpf: fix tail call jumps When a tail call fails, it is documented that the tail call should continue execution at the following instruction. An example tail call sequence is: 12: (85) call bpf_tail_call#12 13: (b7) r0 = 0 14: (95) exit The ARM assembler for the tail call in this case ends up branching to instruction 14 instead of instruction 13, resulting in the BPF filter returning a non-zero value: 178: ldr r8, [sp, #588] ; insn 12 17c: ldr r6, [r8, r6] 180: ldr r8, [sp, #580] 184: cmp r8, r6 188: bcs 0x1e8 18c: ldr r6, [sp, #524] 190: ldr r7, [sp, #528] 194: cmp r7, #0 198: cmpeq r6, #32 19c: bhi 0x1e8 1a0: adds r6, r6, #1 1a4: adc r7, r7, #0 1a8: str r6, [sp, #524] 1ac: str r7, [sp, #528] 1b0: mov r6, #104 1b4: ldr r8, [sp, #588] 1b8: add r6, r8, r6 1bc: ldr r8, [sp, #580] 1c0: lsl r7, r8, #2 1c4: ldr r6, [r6, r7] 1c8: cmp r6, #0 1cc: beq 0x1e8 1d0: mov r8, #32 1d4: ldr r6, [r6, r8] 1d8: add r6, r6, #44 1dc: bx r6 1e0: mov r0, #0 ; insn 13 1e4: mov r1, #0 1e8: add sp, sp, #596 ; insn 14 1ec: pop {r4, r5, r6, r7, r8, sl, pc} For other sequences, the tail call could end up branching midway through the following BPF instructions, or maybe off the end of the function, leading to unknown behaviours. Fixes: 39c13c204bb1 ("arm: eBPF JIT compiler") Signed-off-by: Russell King --- arch/arm/net/bpf_jit_32.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/arm/net') diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c index 4efb374..ce36d2c 100644 --- a/arch/arm/net/bpf_jit_32.c +++ b/arch/arm/net/bpf_jit_32.c @@ -949,7 +949,7 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx) const u8 *tcc = bpf2a32[TCALL_CNT]; const int idx0 = ctx->idx; #define cur_offset (ctx->idx - idx0) -#define jmp_offset (out_offset - (cur_offset)) +#define jmp_offset (out_offset - (cur_offset) - 2) u32 off, lo, hi; /* if (index >= array->map.max_entries) -- cgit v1.1