Re: [bpf-next v8 5/5] bpf, arm64: Emit BTI for indirect jump target

[Anton Protopopov <a.s.protopopov@gmail.com>]

On 26/03/09 10:00PM, Xu Kuohai wrote:
> From: Xu Kuohai <xukuohai@huawei.com>
> 
> On CPUs that support BTI, the indirect jump selftest triggers a kernel
> panic because there is no BTI instructions at the indirect jump targets.
> 
> Fix it by emitting a BTI instruction for each indirect jump target.
> 
> For reference, below is a sample panic log.
> 
> Internal error: Oops - BTI: 0000000036000003 [#1]  SMP
> ...
> Call trace:
>  bpf_prog_2e5f1c71c13ac3e0_big_jump_table+0x54/0xf8 (P)
>  bpf_prog_run_pin_on_cpu+0x140/0x468
>  bpf_prog_test_run_syscall+0x280/0x3b8
>  bpf_prog_test_run+0x22c/0x2c0
> 
> Fixes: f4a66cf1cb14 ("bpf: arm64: Add support for indirect jumps")
> Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
> ---
>  arch/arm64/net/bpf_jit_comp.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> index 5c785eab4b5a..036ad607720a 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -1198,8 +1198,8 @@ static int add_exception_handler(const struct bpf_insn *insn,
>   * >0 - successfully JITed a 16-byte eBPF instruction.
>   * <0 - failed to JIT.
>   */
> -static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
> -		      bool extra_pass)
> +static int build_insn(const struct bpf_verifier_env *env, const struct bpf_insn *insn,
> +		      struct jit_ctx *ctx, bool extra_pass)
>  {
>  	const u8 code = insn->code;
>  	u8 dst = bpf2a64[insn->dst_reg];
> @@ -1224,6 +1224,9 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
>  	int ret;
>  	bool sign_extend;
>  
> +	if (bpf_insn_is_indirect_target(env, ctx->prog, i))
> +		emit_bti(A64_BTI_J, ctx);
> +
>  	switch (code) {
>  	/* dst = src */
>  	case BPF_ALU | BPF_MOV | BPF_X:
> @@ -1899,7 +1902,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
>  	return 0;
>  }
>  
> -static int build_body(struct jit_ctx *ctx, bool extra_pass)
> +static int build_body(struct bpf_verifier_env *env, struct jit_ctx *ctx, bool extra_pass)
>  {
>  	const struct bpf_prog *prog = ctx->prog;
>  	int i;
> @@ -1918,7 +1921,7 @@ static int build_body(struct jit_ctx *ctx, bool extra_pass)
>  		int ret;
>  
>  		ctx->offset[i] = ctx->idx;
> -		ret = build_insn(insn, ctx, extra_pass);
> +		ret = build_insn(env, insn, ctx, extra_pass);
>  		if (ret > 0) {
>  			i++;
>  			ctx->offset[i] = ctx->idx;
> @@ -2086,7 +2089,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
>  	if (build_prologue(&ctx, was_classic))
>  		goto out_off;
>  
> -	if (build_body(&ctx, extra_pass))
> +	if (build_body(env, &ctx, extra_pass))
>  		goto out_off;
>  
>  	ctx.epilogue_offset = ctx.idx;
> @@ -2134,7 +2137,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
>  	/* Dont write body instructions to memory for now */
>  	ctx.write = false;
>  
> -	if (build_body(&ctx, extra_pass))
> +	if (build_body(env, &ctx, extra_pass))
>  		goto out_free_hdr;
>  
>  	ctx.epilogue_offset = ctx.idx;
> @@ -2143,7 +2146,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
>  	ctx.write = true;
>  
>  	/* Pass 3: Adjust jump offset and write final image */
> -	if (build_body(&ctx, extra_pass) ||
> +	if (build_body(env, &ctx, extra_pass) ||
>  		WARN_ON_ONCE(ctx.idx != ctx.epilogue_offset))
>  		goto out_free_hdr;
>  
> -- 
> 2.47.3
> 

Reviewed-by: Anton Protopopov <a.s.protopopov@gmail.com>