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bpf, arm64: fix stack_depth tracking in combination with tail calls

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Using dynamic stack_depth tracking in arm64 JIT is currently broken in
combination with tail calls. In prologue, we cache ctx->stack_size and
adjust SP reg for setting up function call stack, and tearing it down
again in epilogue. Problem is that when doing a tail call, the cached
ctx->stack_size might not be the same.

One way to fix the problem with minimal overhead is to re-adjust SP in
emit_bpf_tail_call() and properly adjust it to the current program's
ctx->stack_size. Tested on Cavium ThunderX ARMv8.

Fixes: f1c9eed7f4 ("bpf, arm64: take advantage of stack_depth tracking")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2018-01-16 03:46:08 +01:00 committed by Alexei Starovoitov
parent 68fda450a7
commit a2284d912b
1 changed files with 11 additions and 9 deletions
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20
arch/arm64/net/bpf_jit_comp.c
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@ -148,7 +148,8 @@ static inline int epilogue_offset(const struct jit_ctx *ctx)
/* Stack must be multiples of 16B */
#define STACK_ALIGN(sz) (((sz) + 15) & ~15)
#define PROLOGUE_OFFSET 8
/* Tail call offset to jump into */
#define PROLOGUE_OFFSET 7
static int build_prologue(struct jit_ctx *ctx)
{
@ -200,19 +201,19 @@ static int build_prologue(struct jit_ctx *ctx)
/* Initialize tail_call_cnt */
emit(A64_MOVZ(1, tcc, 0, 0), ctx);
/* 4 byte extra for skb_copy_bits buffer */
ctx->stack_size = prog->aux->stack_depth + 4;
ctx->stack_size = STACK_ALIGN(ctx->stack_size);
/* Set up function call stack */
emit(A64_SUB_I(1, A64_SP, A64_SP, ctx->stack_size), ctx);
cur_offset = ctx->idx - idx0;
if (cur_offset != PROLOGUE_OFFSET) {
pr_err_once("PROLOGUE_OFFSET = %d, expected %d!\n",
cur_offset, PROLOGUE_OFFSET);
return -1;
}
/* 4 byte extra for skb_copy_bits buffer */
ctx->stack_size = prog->aux->stack_depth + 4;
ctx->stack_size = STACK_ALIGN(ctx->stack_size);
/* Set up function call stack */
emit(A64_SUB_I(1, A64_SP, A64_SP, ctx->stack_size), ctx);
return 0;
}
@ -260,11 +261,12 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx)
emit(A64_LDR64(prg, tmp, prg), ctx);
emit(A64_CBZ(1, prg, jmp_offset), ctx);
/* goto *(prog->bpf_func + prologue_size); */
/* goto *(prog->bpf_func + prologue_offset); */
off = offsetof(struct bpf_prog, bpf_func);
emit_a64_mov_i64(tmp, off, ctx);
emit(A64_LDR64(tmp, prg, tmp), ctx);
emit(A64_ADD_I(1, tmp, tmp, sizeof(u32) * PROLOGUE_OFFSET), ctx);
emit(A64_ADD_I(1, A64_SP, A64_SP, ctx->stack_size), ctx);
emit(A64_BR(tmp), ctx);
/* out: */