Le 01/10/2021 à 23:14, Naveen N. Rao a écrit :
In some scenarios, it is possible that the program epilogue is outside
the branch range for a BPF_EXIT instruction. Instead of rejecting such
programs, emit an indirect branch. We track the size of the bpf program
emitted after the initial run and do a second pass since BPF_EXIT can
end up emitting different number of instructions depending on the
program size.
Suggested-by: Jordan Niethe <jniethe5@xxxxxxxxx>
Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
---
arch/powerpc/net/bpf_jit.h | 3 +++
arch/powerpc/net/bpf_jit_comp.c | 22 +++++++++++++++++++++-
arch/powerpc/net/bpf_jit_comp32.c | 2 +-
arch/powerpc/net/bpf_jit_comp64.c | 2 +-
4 files changed, 26 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index 89bd744c2bffd4..4023de1698b9f5 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -126,6 +126,7 @@
#define SEEN_FUNC 0x20000000 /* might call external helpers */
#define SEEN_TAILCALL 0x40000000 /* uses tail calls */
+#define SEEN_BIG_PROG 0x80000000 /* large prog, >32MB */
#define SEEN_VREG_MASK 0x1ff80000 /* Volatile registers r3-r12 */
#define SEEN_NVREG_MASK 0x0003ffff /* Non volatile registers r14-r31 */
@@ -179,6 +180,8 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx);
void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx);
void bpf_jit_realloc_regs(struct codegen_context *ctx);
+int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx,
+ int tmp_reg, unsigned long exit_addr);
#endif
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index fcbf7a917c566e..3204872fbf2738 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -72,6 +72,21 @@ static int bpf_jit_fixup_subprog_calls(struct bpf_prog *fp, u32 *image,
return 0;
}
+int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx,
+ int tmp_reg, unsigned long exit_addr)
+{
+ if (!(ctx->seen & SEEN_BIG_PROG) && is_offset_in_branch_range(exit_addr)) {
+ PPC_JMP(exit_addr);
+ } else {
+ ctx->seen |= SEEN_BIG_PROG;
+ PPC_FUNC_ADDR(tmp_reg, (unsigned long)image + exit_addr);
+ EMIT(PPC_RAW_MTCTR(tmp_reg));
+ EMIT(PPC_RAW_BCTR());
+ }
+
+ return 0;
+}
+
struct powerpc64_jit_data {
struct bpf_binary_header *header;
u32 *addrs;
@@ -155,12 +170,17 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
goto out_addrs;
}
+ if (!is_offset_in_branch_range((long)cgctx.idx * 4))
+ cgctx.seen |= SEEN_BIG_PROG;
+
/*
* If we have seen a tail call, we need a second pass.
* This is because bpf_jit_emit_common_epilogue() is called
* from bpf_jit_emit_tail_call() with a not yet stable ctx->seen.
+ * We also need a second pass if we ended up with too large
+ * a program so as to fix branches.
*/
- if (cgctx.seen & SEEN_TAILCALL) {
+ if (cgctx.seen & (SEEN_TAILCALL | SEEN_BIG_PROG)) {
cgctx.idx = 0;
if (bpf_jit_build_body(fp, 0, &cgctx, addrs, false)) {
fp = org_fp;
diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index a74d52204f8da2..d2a67574a23066 100644
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -852,7 +852,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
* we'll just fall through to the epilogue.
*/
if (i != flen - 1)
- PPC_JMP(exit_addr);
+ bpf_jit_emit_exit_insn(image, ctx, tmp_reg, exit_addr);
On ppc32, if you use tmp_reg you must flag it. But I think you could use
r0 instead.
/* else fall through to the epilogue */
break;
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index f06c62089b1457..3351a866ef6207 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -761,7 +761,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
* we'll just fall through to the epilogue.
*/
if (i != flen - 1)
- PPC_JMP(exit_addr);
+ bpf_jit_emit_exit_insn(image, ctx, b2p[TMP_REG_1], exit_addr);
/* else fall through to the epilogue */
break;
