diff --git a/arch/powerpc/net/bpf_jit_comp64.c
b/arch/powerpc/net/bpf_jit_comp64.c
index db121b1404fe..17de8b53a962 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
[ ... ]
+/*
+ * For exception boundary & exception_cb progs:
+ * return increased size to accommodate additional NVRs.
+ */
+static int bpf_jit_stack_size(struct codegen_context *ctx)
+{
+ return ctx->exception_boundary || ctx->exception_cb ?
+ BPF_PPC_EXC_STACKFRAME :
+ BPF_PPC_STACKFRAME;
+}
[ ... ]
@@ -198,7 +249,19 @@ void bpf_jit_build_prologue(u32 *image, struct
codegen_context *ctx)
EMIT(PPC_RAW_STD(_R0, _R1, PPC_LR_STKOFF));
}
- EMIT(PPC_RAW_STDU(_R1, _R1, -(BPF_PPC_STACKFRAME +
ctx->stack_size)));
+ EMIT(PPC_RAW_STDU(_R1, _R1,
+ -(bpf_jit_stack_size(ctx) + ctx->stack_size)));
+ }
[ ... ]
@@ -248,9 +311,19 @@ static void bpf_jit_emit_common_epilogue(u32 *image,
struct codegen_context *ctx)
EMIT(PPC_RAW_LD(bpf_to_ppc(ARENA_VM_START), _R1,
bpf_jit_stack_offsetof(ctx,
bpf_to_ppc(ARENA_VM_START))));
+ if (ctx->exception_cb) {
+ /*
+ * Recover additionally saved non volatile registers from stack
+ * frame of exception boundary program.
+ */
+ for (i = _R14; i <= _R25; i++)
+ EMIT(PPC_RAW_LD(i, _R1, bpf_jit_stack_offsetof(ctx,
i)));
+ }
+
/* Tear down our stack frame */
if (bpf_has_stack_frame(ctx)) {
- EMIT(PPC_RAW_ADDI(_R1, _R1, BPF_PPC_STACKFRAME +
ctx->stack_size));
+ EMIT(PPC_RAW_ADDI(_R1, _R1, bpf_jit_stack_size(ctx) +
ctx->stack_size));
For the exception callback case, doesn't this use the wrong stack_size?
In bpf_jit_build_prologue(), the exception callback does not create its own
frame - it sets R1 to the boundary's frame pointer via EMIT(PPC_RAW_MR(_R1,
_R5)). However here in the epilogue, the frame teardown uses ctx->stack_size
which is the callback's stack depth, not the boundary's.
The boundary program creates its frame with:
STDU R1, R1, -(bpf_jit_stack_size(boundary_ctx) + boundary_stack_size)
But the callback tears it down with:
ADDI R1, R1, bpf_jit_stack_size(callback_ctx) + callback_stack_size
Since each BPF subprogram can have a different stack_depth (set per-subprog
in kernel/bpf/verifier.c via func[i]->aux->stack_depth), if the exception
callback has a different stack depth than the boundary, R1 will end up at
the wrong location after this ADDI.
After the wrong R1 adjustment, the LR restore below loads from R1+16 which
is now pointing to the wrong memory location, potentially causing a return
to an invalid address.
Would it be correct to store the boundary's stack_size somewhere accessible
to the callback, or ensure the callback uses the same stack layout as the
boundary?
+
if (ctx->seen & SEEN_FUNC || ctx->exception_cb) {
EMIT(PPC_RAW_LD(_R0, _R1, PPC_LR_STKOFF));
EMIT(PPC_RAW_MTLR(_R0));
---
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