diff mbox series

[v5,1/6] powerpc/bpf: fix alignment of long branch trampoline address

Message ID 20260519233812.18787-2-adubey@linux.ibm.com (mailing list archive)
State Superseded
Headers show
Series powerpc/bpf: Add support for verifier selftest | expand

Commit Message

adubey May 19, 2026, 11:38 p.m. UTC 
From: Abhishek Dubey <adubey@linux.ibm.com>

Ensure the dummy trampoline address field present between the OOL stub
and the long branch stub is 8-byte aligned, for memory compatibility
when content loaded to a register.

Reported-by: Hari Bathini <hbathini@linux.ibm.com>
Fixes: d243b62b7bd3 ("powerpc64/bpf: Add support for bpf trampolines")
Cc: stable@vger.kernel.org
Signed-off-by: Abhishek Dubey <adubey@linux.ibm.com>
---
 arch/powerpc/net/bpf_jit.h        |  4 ++--
 arch/powerpc/net/bpf_jit_comp.c   | 38 +++++++++++++++++++++++++++----
 arch/powerpc/net/bpf_jit_comp32.c |  4 ++--
 arch/powerpc/net/bpf_jit_comp64.c |  4 ++--
 4 files changed, 39 insertions(+), 11 deletions(-)
diff mbox series

Patch

diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index f32de8704d4d..71e6e7d01057 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -214,8 +214,8 @@  int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *
 int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct codegen_context *ctx,
 		       u32 *addrs, int pass, bool extra_pass);
 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_build_fentry_stubs(u32 *image, struct codegen_context *ctx);
+void bpf_jit_build_epilogue(u32 *image, u32 *fimage, struct codegen_context *ctx);
+void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage, 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, long exit_addr);
 void prepare_for_fsession_fentry(u32 *image, struct codegen_context *ctx, int cookie_cnt,
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 53ab97ad6074..00b86ed97cb5 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -49,11 +49,38 @@  asm (
 "	.popsection				;"
 );
 
-void bpf_jit_build_fentry_stubs(u32 *image, struct codegen_context *ctx)
+void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage, struct codegen_context *ctx)
 {
 	int ool_stub_idx, long_branch_stub_idx;
+	int ool_instrs;
 
 	/*
+	 * In the final pass, align the mis-aligned dummy_tramp_addr field
+	 * in the fimage. The alignment NOP must appear before OOL stub,
+	 * to make ool_stub_idx & long_branch_stub_idx constant from end.
+	 *
+	 * dummy_tramp_addr must be 8-byte aligned for load-register
+	 * compatibility. Since fimage is guaranteed >= 8-byte aligned
+	 * by the allocator, alignment depends only on the instruction
+	 * count offset. The OOL stub has 4 instructions (with
+	 * CONFIG_PPC_FTRACE_OUT_OF_LINE) or 3 instructions (without)
+	 * before dummy_tramp_addr.
+	 *
+	 * Emit a NOP here if (ctx->idx + ool_instrs) is odd, so that
+	 * dummy_tramp_addr lands at an even instruction offset (== 8-byte
+	 * aligned from an 8-byte aligned base).
+	 *
+	 * In pass=0 when image==NULL, conservatively account for space
+	 * required to accommodate alignment NOP. In case final pass skips
+	 * emitting alignment NOP, the image buffer have 4 spare bytes and
+	 * jited_len signifies correct program size.
+	 */
+
+	ool_instrs = IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 4 : 3;
+	if (!image || ((ctx->idx + ool_instrs) & 1))
+		EMIT(PPC_RAW_NOP());
+
+	/*      nop     // optional, for alignment of dummy_tramp_addr
 	 * Out-of-line stub:
 	 *	mflr	r0
 	 *	[b|bl]	tramp
@@ -70,7 +97,7 @@  void bpf_jit_build_fentry_stubs(u32 *image, struct codegen_context *ctx)
 
 	/*
 	 * Long branch stub:
-	 *	.long	<dummy_tramp_addr>
+	 *	.long	<dummy_tramp_addr>  // 8-byte aligned
 	 *	mflr	r11
 	 *	bcl	20,31,$+4
 	 *	mflr	r12
@@ -81,6 +108,7 @@  void bpf_jit_build_fentry_stubs(u32 *image, struct codegen_context *ctx)
 	 */
 	if (image)
 		*((unsigned long *)&image[ctx->idx]) = (unsigned long)dummy_tramp;
+
 	ctx->idx += SZL / 4;
 	long_branch_stub_idx = ctx->idx;
 	EMIT(PPC_RAW_MFLR(_R11));
@@ -107,7 +135,7 @@  int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx, int tmp_reg,
 		PPC_JMP(ctx->alt_exit_addr);
 	} else {
 		ctx->alt_exit_addr = ctx->idx * 4;
-		bpf_jit_build_epilogue(image, ctx);
+		bpf_jit_build_epilogue(image, NULL, ctx);
 	}
 
 	return 0;
@@ -286,7 +314,7 @@  struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
 	 */
 	bpf_jit_build_prologue(NULL, &cgctx);
 	addrs[fp->len] = cgctx.idx * 4;
-	bpf_jit_build_epilogue(NULL, &cgctx);
+	bpf_jit_build_epilogue(NULL, NULL, &cgctx);
 
 	fixup_len = fp->aux->num_exentries * BPF_FIXUP_LEN * 4;
 	extable_len = fp->aux->num_exentries * sizeof(struct exception_table_entry);
@@ -318,7 +346,7 @@  struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
 			bpf_jit_binary_pack_free(fhdr, hdr);
 			goto out_err;
 		}
-		bpf_jit_build_epilogue(code_base, &cgctx);
+		bpf_jit_build_epilogue(code_base, fcode_base, &cgctx);
 
 		if (bpf_jit_enable > 1)
 			pr_info("Pass %d: shrink = %d, seen = 0x%x\n", pass,
diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index bfdc50740da8..95bda0dee925 100644
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -229,7 +229,7 @@  static void bpf_jit_emit_common_epilogue(u32 *image, struct codegen_context *ctx
 
 }
 
-void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
+void bpf_jit_build_epilogue(u32 *image, u32 *fimage, struct codegen_context *ctx)
 {
 	EMIT(PPC_RAW_MR(_R3, bpf_to_ppc(BPF_REG_0)));
 
@@ -237,7 +237,7 @@  void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
 
 	EMIT(PPC_RAW_BLR());
 
-	bpf_jit_build_fentry_stubs(image, ctx);
+	bpf_jit_build_fentry_stubs(image, fimage, ctx);
 }
 
 /* Relative offset needs to be calculated based on final image location */
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index db364d9083e7..885dc8cf55a2 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -398,7 +398,7 @@  static void bpf_jit_emit_common_epilogue(u32 *image, struct codegen_context *ctx
 	}
 }
 
-void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
+void bpf_jit_build_epilogue(u32 *image, u32 *fimage, struct codegen_context *ctx)
 {
 	bpf_jit_emit_common_epilogue(image, ctx);
 
@@ -407,7 +407,7 @@  void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
 
 	EMIT(PPC_RAW_BLR());
 
-	bpf_jit_build_fentry_stubs(image, ctx);
+	bpf_jit_build_fentry_stubs(image, fimage, ctx);
 }
 
 /*