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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        "ast@kernel.org, stable@vger.kernel.org, Daniel Borkmann" 
        <daniel@iogearbox.net>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>
Subject: [PATCH 4.14 70/71] bpf, arm64: fix stack_depth tracking in combination with tail calls
Date:   Mon, 29 Jan 2018 13:57:38 +0100
Message-Id: <20180129123832.239908860@linuxfoundation.org>
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References: <20180129123827.271171825@linuxfoundation.org>
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4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Borkmann <daniel@iogearbox.net>

[ upstream commit a2284d912bfc865cdca4c00488e08a3550f9a405 ]

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: f1c9eed7f437 ("bpf, arm64: take advantage of stack_depth tracking")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/arm64/net/bpf_jit_comp.c |   20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -148,7 +148,8 @@ static inline int epilogue_offset(const
 /* 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
 	/* 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
 	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: */