Re: [PATCH v2 1/2] powerpc/bpf: ensure module addresses are supported

Hari Bathini <hbathini@xxxxxxxxxxxxx> · Thu, 15 Feb 2024 16:07:56 +0530

On 13/02/24 1:23 pm, Christophe Leroy wrote:


Le 01/02/2024 à 18:12, Hari Bathini a écrit :
Currently, bpf jit code on powerpc assumes all the bpf functions and
helpers to be kernel text. This is false for kfunc case, as function
addresses are mostly module addresses in that case. Ensure module
addresses are supported to enable kfunc support.

Assume kernel text address for programs with no kfunc call to optimize
instruction sequence in that case. Add a check to error out if this
assumption ever changes in the future.

Signed-off-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>
---

Changes in v2:
* Using bpf_prog_has_kfunc_call() to decide whether to use optimized
    instruction sequence or not as suggested by Naveen.


   arch/powerpc/net/bpf_jit.h        |   5 +-
   arch/powerpc/net/bpf_jit_comp.c   |   4 +-
   arch/powerpc/net/bpf_jit_comp32.c |   8 ++-
   arch/powerpc/net/bpf_jit_comp64.c | 109 ++++++++++++++++++++++++------
   4 files changed, 97 insertions(+), 29 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index cdea5dccaefe..fc56ee0ee9c5 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -160,10 +160,11 @@ static inline void bpf_clear_seen_register(struct codegen_context *ctx, int i)
   }
   
   void bpf_jit_init_reg_mapping(struct codegen_context *ctx);
-int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func);
+int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func,
+			       bool has_kfunc_call);
   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_prologue(u32 *image, struct codegen_context *ctx, bool has_kfunc_call);
   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, long exit_addr);
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 0f9a21783329..7b4103b4c929 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -163,7 +163,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
   	 * update ctgtx.idx as it pretends to output instructions, then we can
   	 * calculate total size from idx.
   	 */
-	bpf_jit_build_prologue(NULL, &cgctx);
+	bpf_jit_build_prologue(NULL, &cgctx, bpf_prog_has_kfunc_call(fp));
   	addrs[fp->len] = cgctx.idx * 4;
   	bpf_jit_build_epilogue(NULL, &cgctx);
   
@@ -192,7 +192,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
   		/* Now build the prologue, body code & epilogue for real. */
   		cgctx.idx = 0;
   		cgctx.alt_exit_addr = 0;
-		bpf_jit_build_prologue(code_base, &cgctx);
+		bpf_jit_build_prologue(code_base, &cgctx, bpf_prog_has_kfunc_call(fp));
   		if (bpf_jit_build_body(fp, code_base, fcode_base, &cgctx, addrs, pass,
   				       extra_pass)) {
   			bpf_arch_text_copy(&fhdr->size, &hdr->size, sizeof(hdr->size));
diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index 2f39c50ca729..447747e51a58 100644
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -123,7 +123,7 @@ void bpf_jit_realloc_regs(struct codegen_context *ctx)
   	}
   }
   
-void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
+void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx, bool has_kfunc_call)
   {
   	int i;
   
@@ -201,7 +201,8 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
   }
   
   /* Relative offset needs to be calculated based on final image location */
-int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func)
+int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func,
+			       bool has_kfunc_call)
   {
   	s32 rel = (s32)func - (s32)(fimage + ctx->idx);
   
@@ -1054,7 +1055,8 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
   				EMIT(PPC_RAW_STW(bpf_to_ppc(BPF_REG_5), _R1, 12));
   			}
   
-			ret = bpf_jit_emit_func_call_rel(image, fimage, ctx, func_addr);
+			ret = bpf_jit_emit_func_call_rel(image, fimage, ctx, func_addr,
+							 bpf_prog_has_kfunc_call(fp));
   			if (ret)
   				return ret;
   
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 79f23974a320..385a5df1670c 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -122,12 +122,17 @@ void bpf_jit_realloc_regs(struct codegen_context *ctx)
   {
   }
   
-void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
+void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx, bool has_kfunc_call)
   {
   	int i;
   
   #ifndef CONFIG_PPC_KERNEL_PCREL
-	if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2))
+	/*
+	 * If the program doesn't have a kfunc call, all BPF helpers are part of kernel text
+	 * and all BPF programs/functions utilize the kernel TOC. So, optimize the
+	 * instruction sequence by using kernel toc in r2 for that case.
+	 */
+	if (!has_kfunc_call && IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2))
   		EMIT(PPC_RAW_LD(_R2, _R13, offsetof(struct paca_struct, kernel_toc)));
   #endif
   
@@ -202,12 +207,17 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
   	EMIT(PPC_RAW_BLR());
   }
   
-static int bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx, u64 func)
+static int bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx, u64 func,
+				      bool has_kfunc_call)
   {
   	unsigned long func_addr = func ? ppc_function_entry((void *)func) : 0;
   	long reladdr;
   
-	if (WARN_ON_ONCE(!core_kernel_text(func_addr)))
+	/*
+	 * If the program doesn't have a kfunc call, all BPF helpers are assumed to be part of
+	 * kernel text. Don't proceed if that assumption ever changes in future.
+	 */
+	if (!has_kfunc_call && WARN_ON_ONCE(!core_kernel_text(func_addr)))
   		return -EINVAL;
   
   	if (IS_ENABLED(CONFIG_PPC_KERNEL_PCREL)) {
@@ -225,30 +235,55 @@ static int bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx, u
   		EMIT(PPC_RAW_BCTR());
   
   	} else {
-		reladdr = func_addr - kernel_toc_addr();
-		if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
-			pr_err("eBPF: address of %ps out of range of kernel_toc.\n", (void *)func);
-			return -ERANGE;
-		}
+		if (has_kfunc_call) {
+#ifdef PPC64_ELF_ABI_v1

I can't see a reason for a #ifdef here, why not use IS_ENABLED() like
other places ?

+			/* func points to the function descriptor */
+			PPC_LI64(b2p[TMP_REG_2], func);
+			/* Load actual entry point from function descriptor */
+			PPC_BPF_LL(b2p[TMP_REG_1], b2p[TMP_REG_2], 0);
+			/* ... and move it to CTR */
+			EMIT(PPC_RAW_MTCTR(b2p[TMP_REG_1]));
+			/*
+			 * Load TOC from function descriptor at offset 8.
+			 * We can clobber r2 since we get called through a
+			 * function pointer (so caller will save/restore r2)
+			 * and since we don't use a TOC ourself.
+			 */
+			PPC_BPF_LL(2, b2p[TMP_REG_2], 8);
+#else
+			/* We can clobber r12 */
+			PPC_LI64(12, func);
+			EMIT(PPC_RAW_MTCTR(12));
+#endif
+		} else {
+			reladdr = func_addr - kernel_toc_addr();
+			if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) {
+				pr_err("eBPF: address of %ps out of range of kernel_toc.\n",
+				       (void *)func);
+				return -ERANGE;
+			}
   
-		EMIT(PPC_RAW_ADDIS(_R12, _R2, PPC_HA(reladdr)));
-		EMIT(PPC_RAW_ADDI(_R12, _R12, PPC_LO(reladdr)));
-		EMIT(PPC_RAW_MTCTR(_R12));
+			EMIT(PPC_RAW_ADDIS(_R12, _R2, PPC_HA(reladdr)));
+			EMIT(PPC_RAW_ADDI(_R12, _R12, PPC_LO(reladdr)));
+			EMIT(PPC_RAW_MTCTR(_R12));
+		}
   		EMIT(PPC_RAW_BCTRL());
   	}
   
   	return 0;
   }
   
-int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func)
+int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func,
+			       bool has_kfunc_call)
   {
   	unsigned int i, ctx_idx = ctx->idx;
   
-	if (WARN_ON_ONCE(func && is_module_text_address(func)))
+	if (WARN_ON_ONCE(func && !has_kfunc_call && is_module_text_address(func)))
   		return -EINVAL;
   
   	/* skip past descriptor if elf v1 */
-	func += FUNCTION_DESCR_SIZE;
+	if (!has_kfunc_call)
+		func += FUNCTION_DESCR_SIZE;
   
   	/* Load function address into r12 */
   	PPC_LI64(_R12, func);
@@ -267,13 +302,28 @@ int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *
   		for (i = ctx->idx - ctx_idx; i < 5; i++)
   			EMIT(PPC_RAW_NOP());
   
+#ifdef PPC64_ELF_ABI_v1

I can't see a reason for a #ifdef here, why not use IS_ENABLED() like
other places ?

Will update.



+	if (has_kfunc_call) {
+		/*
+		 * Load TOC from function descriptor at offset 8.
+		 * We can clobber r2 since we get called through a
+		 * function pointer (so caller will save/restore r2)
+		 * and since we don't use a TOC ourself.
+		 */
+		PPC_BPF_LL(2, 12, 8);
+		/* Load actual entry point from function descriptor */
+		PPC_BPF_LL(12, 12, 0);
+	}
+#endif
+
   	EMIT(PPC_RAW_MTCTR(_R12));
   	EMIT(PPC_RAW_BCTRL());
   
   	return 0;
   }
   
-static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 out)
+static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 out,
+				  bool has_kfunc_call)
   {
   	/*
   	 * By now, the eBPF program has already setup parameters in r3, r4 and r5
@@ -285,7 +335,7 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
   	int b2p_index = bpf_to_ppc(BPF_REG_3);
   	int bpf_tailcall_prologue_size = 8;
   
-	if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2))
+	if (!has_kfunc_call && IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2))
   		bpf_tailcall_prologue_size += 4; /* skip past the toc load */
   
   	/*
@@ -325,8 +375,20 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
   
   	/* goto *(prog->bpf_func + prologue_size); */
   	EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1), offsetof(struct bpf_prog, bpf_func)));
-	EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1),
-			FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
+	if (has_kfunc_call) {
+#ifdef PPC64_ELF_ABI_v1

I can't see a reason for a #ifdef here, why not use IS_ENABLED() like
other places ?

+		/* skip past the function descriptor */
+		EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1),
+				FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
+#else
+		EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1),
+				bpf_tailcall_prologue_size));
+#endif
+	} else {
+		EMIT(PPC_RAW_ADDI(bpf_to_ppc(TMP_REG_1), bpf_to_ppc(TMP_REG_1),
+				FUNCTION_DESCR_SIZE + bpf_tailcall_prologue_size));
+	}
+
   	EMIT(PPC_RAW_MTCTR(bpf_to_ppc(TMP_REG_1)));
   
   	/* tear down stack, restore NVRs, ... */
@@ -365,6 +427,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
   		       u32 *addrs, int pass, bool extra_pass)
   {
   	enum stf_barrier_type stf_barrier = stf_barrier_type_get();
+	bool has_kfunc_call = bpf_prog_has_kfunc_call(fp);
   	const struct bpf_insn *insn = fp->insnsi;
   	int flen = fp->len;
   	int i, ret;
@@ -993,9 +1056,11 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
   				return ret;
   
   			if (func_addr_fixed)
-				ret = bpf_jit_emit_func_call_hlp(image, ctx, func_addr);
+				ret = bpf_jit_emit_func_call_hlp(image, ctx, func_addr,
+								 has_kfunc_call);

Doesn't this fit on a single line ?

   			else
-				ret = bpf_jit_emit_func_call_rel(image, fimage, ctx, func_addr);
+				ret = bpf_jit_emit_func_call_rel(image, fimage, ctx, func_addr,
+								 has_kfunc_call);

Same. Nowadays lines up to 100 chars are the norm.

Goes beyond 100 chars.


   
   			if (ret)
   				return ret;
@@ -1204,7 +1269,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
   		 */
   		case BPF_JMP | BPF_TAIL_CALL:
   			ctx->seen |= SEEN_TAILCALL;
-			ret = bpf_jit_emit_tail_call(image, ctx, addrs[i + 1]);
+			ret = bpf_jit_emit_tail_call(image, ctx, addrs[i + 1], has_kfunc_call);
   			if (ret < 0)
   				return ret;
   			break;

Thanks
Hari







