arm64: bpf: fix buffer pointer

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@gmail.com>
Acked-by: Yang Shi <yang.shi@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 14 deletions

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index d6a53ef2350b..7cf032bebf8c 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);
                 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);