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authorYang Shi <yang.shi@linaro.org>2015-11-16 14:35:35 -0800
committerDavid S. Miller <davem@davemloft.net>2015-11-17 14:44:39 -0500
commitec0738db8d7a9bd6653d9f9d81b201a519144d63 (patch)
treeab7bd5c2ac7e695b3c463ee4fb21a816be409d50 /arch
parente639b8d8a7a728f0b05ef2df6cb6b45dc3d4e556 (diff)
downloadlinux-sh-ec0738db8d7a9bd6653d9f9d81b201a519144d63.tar.gz
arm64: bpf: make BPF prologue and epilogue align with ARM64 AAPCS
Save and restore FP/LR in BPF prog prologue and epilogue, save SP to FP in prologue in order to get the correct stack backtrace. However, ARM64 JIT used FP (x29) as eBPF fp register, FP is subjected to change during function call so it may cause the BPF prog stack base address change too. Use x25 to replace FP as BPF stack base register (fp). Since x25 is callee saved register, so it will keep intact during function call. It is initialized in BPF prog prologue when BPF prog is started to run everytime. Save and restore x25/x26 in BPF prologue and epilogue to keep them intact for the outside of BPF. Actually, x26 is unnecessary, but SP requires 16 bytes alignment. So, the BPF stack layout looks like: high original A64_SP => 0:+-----+ BPF prologue |FP/LR| current A64_FP => -16:+-----+ | ... | callee saved registers +-----+ | | x25/x26 BPF fp register => -80:+-----+ | | | ... | BPF prog stack | | | | current A64_SP => +-----+ | | | ... | Function call stack | | +-----+ low CC: Zi Shen Lim <zlim.lnx@gmail.com> CC: Xi Wang <xi.wang@gmail.com> Signed-off-by: Yang Shi <yang.shi@linaro.org> Acked-by: Zi Shen Lim <zlim.lnx@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'arch')
-rw-r--r--arch/arm64/net/bpf_jit_comp.c44
1 files changed, 39 insertions, 5 deletions
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 64a8bc12f4a2..a6905b8d12d3 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -50,7 +50,7 @@ static const int bpf2a64[] = {
[BPF_REG_8] = A64_R(21),
[BPF_REG_9] = A64_R(22),
/* read-only frame pointer to access stack */
- [BPF_REG_FP] = A64_FP,
+ [BPF_REG_FP] = A64_R(25),
/* temporary register for internal BPF JIT */
[TMP_REG_1] = A64_R(23),
[TMP_REG_2] = A64_R(24),
@@ -155,16 +155,47 @@ static void build_prologue(struct jit_ctx *ctx)
stack_size += 4; /* extra for skb_copy_bits buffer */
stack_size = STACK_ALIGN(stack_size);
+ /*
+ * BPF prog stack layout
+ *
+ * high
+ * original A64_SP => 0:+-----+ BPF prologue
+ * |FP/LR|
+ * current A64_FP => -16:+-----+
+ * | ... | callee saved registers
+ * +-----+
+ * | | x25/x26
+ * BPF fp register => -80:+-----+
+ * | |
+ * | ... | BPF prog stack
+ * | |
+ * | |
+ * current A64_SP => +-----+
+ * | |
+ * | ... | Function call stack
+ * | |
+ * +-----+
+ * low
+ *
+ */
+
+ /* Save FP and LR registers to stay align with ARM64 AAPCS */
+ emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx);
+ emit(A64_MOV(1, A64_FP, A64_SP), ctx);
+
/* Save callee-saved register */
emit(A64_PUSH(r6, r7, A64_SP), ctx);
emit(A64_PUSH(r8, r9, A64_SP), ctx);
if (ctx->tmp_used)
emit(A64_PUSH(tmp1, tmp2, A64_SP), ctx);
- /* Set up frame pointer */
+ /* Save fp (x25) and x26. SP requires 16 bytes alignment */
+ emit(A64_PUSH(fp, A64_R(26), A64_SP), ctx);
+
+ /* Set up BPF prog stack base register (x25) */
emit(A64_MOV(1, fp, A64_SP), ctx);
- /* Set up BPF stack */
+ /* Set up function call stack */
emit(A64_SUB_I(1, A64_SP, A64_SP, stack_size), ctx);
/* Clear registers A and X */
@@ -190,14 +221,17 @@ static void build_epilogue(struct jit_ctx *ctx)
/* We're done with BPF stack */
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);
+
/* Restore callee-saved register */
if (ctx->tmp_used)
emit(A64_POP(tmp1, tmp2, A64_SP), ctx);
emit(A64_POP(r8, r9, A64_SP), ctx);
emit(A64_POP(r6, r7, A64_SP), ctx);
- /* Restore frame pointer */
- emit(A64_MOV(1, fp, A64_SP), ctx);
+ /* Restore FP/LR registers */
+ emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx);
/* Set return value */
emit(A64_MOV(1, A64_R(0), r0), ctx);