Re: [PATCH] arm64: bpf: fix buffer pointer
From: Shi, Yang
Date: Wed Nov 18 2015 - 16:07:32 EST
On 11/18/2015 12:56 AM, Zi Shen Lim wrote:
During code review, I noticed we were passing a bad buffer pointer
to bpf_load_pointer helper function called by jitted code.
Point to the buffer allocated by JIT, so we don't silently corrupt
other parts of the stack.
Signed-off-by: Zi Shen Lim <zlim.lnx@xxxxxxxxx>
---
arch/arm64/net/bpf_jit_comp.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index d6a53ef..7cf032b 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -139,6 +139,12 @@ static inline int epilogue_offset(const struct jit_ctx *ctx)
/* Stack must be multiples of 16B */
#define STACK_ALIGN(sz) (((sz) + 15) & ~15)
+#define _STACK_SIZE \
+ (MAX_BPF_STACK \
+ + 4 /* extra for skb_copy_bits buffer */)
+
+#define STACK_SIZE STACK_ALIGN(_STACK_SIZE)
+
static void build_prologue(struct jit_ctx *ctx)
{
const u8 r6 = bpf2a64[BPF_REG_6];
@@ -150,10 +156,6 @@ static void build_prologue(struct jit_ctx *ctx)
const u8 rx = bpf2a64[BPF_REG_X];
const u8 tmp1 = bpf2a64[TMP_REG_1];
const u8 tmp2 = bpf2a64[TMP_REG_2];
- int stack_size = MAX_BPF_STACK;
-
- stack_size += 4; /* extra for skb_copy_bits buffer */
- stack_size = STACK_ALIGN(stack_size);
/*
* BPF prog stack layout
@@ -165,12 +167,13 @@ static void build_prologue(struct jit_ctx *ctx)
* | ... | callee saved registers
* +-----+
* | | x25/x26
- * BPF fp register => -80:+-----+
+ * BPF fp register => -80:+-----+ <= (BPF_FP)
* | |
* | ... | BPF prog stack
* | |
- * | |
- * current A64_SP => +-----+
+ * +-----+ <= (BPF_FP - MAX_BPF_STACK)
+ * |RSVD | JIT scratchpad
+ * current A64_SP => +-----+ <= (BPF_FP - STACK_SIZE)
* | |
* | ... | Function call stack
* | |
@@ -196,7 +199,7 @@ static void build_prologue(struct jit_ctx *ctx)
emit(A64_MOV(1, fp, A64_SP), ctx);
/* Set up function call stack */
- emit(A64_SUB_I(1, A64_SP, A64_SP, stack_size), ctx);
+ emit(A64_SUB_I(1, A64_SP, A64_SP, STACK_SIZE), ctx);
/* Clear registers A and X */
emit_a64_mov_i64(ra, 0, ctx);
@@ -213,13 +216,9 @@ static void build_epilogue(struct jit_ctx *ctx)
const u8 fp = bpf2a64[BPF_REG_FP];
const u8 tmp1 = bpf2a64[TMP_REG_1];
const u8 tmp2 = bpf2a64[TMP_REG_2];
- int stack_size = MAX_BPF_STACK;
-
- stack_size += 4; /* extra for skb_copy_bits buffer */
- stack_size = STACK_ALIGN(stack_size);
/* We're done with BPF stack */
- emit(A64_ADD_I(1, A64_SP, A64_SP, stack_size), ctx);
+ emit(A64_ADD_I(1, A64_SP, A64_SP, STACK_SIZE), ctx);
/* Restore fs (x25) and x26 */
emit(A64_POP(fp, A64_R(26), A64_SP), ctx);
@@ -658,7 +657,7 @@ emit_cond_jmp:
return -EINVAL;
}
emit_a64_mov_i64(r3, size, ctx);
- emit(A64_ADD_I(1, r4, fp, MAX_BPF_STACK), ctx);
+ emit(A64_SUB_I(1, r4, fp, STACK_SIZE), ctx);
Should not it sub MAX_BPF_STACK?
If you sub STACK_SIZE here, the buffer pointer will point to bottom of
the reserved area.
You stack layout change also shows this:
+ * +-----+ <= (BPF_FP - MAX_BPF_STACK)
+ * |RSVD | JIT scratchpad
+ * current A64_SP => +-----+ <= (BPF_FP - STACK_SIZE)
Thanks,
Yang
emit_a64_mov_i64(r5, (unsigned long)bpf_load_pointer, ctx);
emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx);
emit(A64_MOV(1, A64_FP, A64_SP), ctx);
--
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