powerpc64/bpf elfv1: Do not load TOC before calling functions

BPF helpers always reside in core kernel and all BPF programs use the
kernel TOC. As such, there is no need to load the TOC before calling
helpers or other BPF functions. Drop code to do the same.

Add a check to ensure we don't proceed if this assumption ever changes
in future.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a3cd3da4d24d95d845cd10382b1af083600c9074.1644834730.git.naveen.n.rao@linux.vnet.ibm.com

arch/powerpc/net/bpf_jit.h

@@ -178,7 +178,7 @@ static inline void bpf_clear_seen_register(struct codegen_context *ctx, int i)
 	ctx->seen &= ~(1 << (31 - i));
 }
 
-void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func);
+int bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func);
 int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *ctx,
 		       u32 *addrs, int pass);
 void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx);

arch/powerpc/net/bpf_jit_comp.c

@@ -59,7 +59,9 @@ static int bpf_jit_fixup_addresses(struct bpf_prog *fp, u32 *image,
 			 */
 			tmp_idx = ctx->idx;
 			ctx->idx = addrs[i] / 4;
-			bpf_jit_emit_func_call_rel(image, ctx, func_addr);
+			ret = bpf_jit_emit_func_call_rel(image, ctx, func_addr);
+			if (ret)
+				return ret;
 
 			/*
 			 * Restore ctx->idx here. This is safe as the length

arch/powerpc/net/bpf_jit_comp32.c

@@ -193,7 +193,7 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
 	EMIT(PPC_RAW_BLR());
 }
 
-void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func)
+int bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func)
 {
 	s32 rel = (s32)func - (s32)(image + ctx->idx);
 
@@ -209,6 +209,8 @@ void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 fun
 		EMIT(PPC_RAW_MTCTR(_R0));
 		EMIT(PPC_RAW_BCTRL());
 	}
+
+	return 0;
 }
 
 static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 out)
@@ -961,7 +963,9 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 				EMIT(PPC_RAW_STW(bpf_to_ppc(ctx, BPF_REG_5), _R1, 12));
 			}
 
-			bpf_jit_emit_func_call_rel(image, ctx, func_addr);
+			ret = bpf_jit_emit_func_call_rel(image, ctx, func_addr);
+			if (ret)
+				return ret;
 
 			EMIT(PPC_RAW_MR(bpf_to_ppc(ctx, BPF_REG_0) - 1, _R3));
 			EMIT(PPC_RAW_MR(bpf_to_ppc(ctx, BPF_REG_0), _R4));

arch/powerpc/net/bpf_jit_comp64.c

@@ -147,9 +147,13 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
 	EMIT(PPC_RAW_BLR());
 }
 
-static void 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)
 {
+	unsigned long func_addr = func ? ppc_function_entry((void *)func) : 0;
+
+	if (WARN_ON_ONCE(!core_kernel_text(func_addr)))
+		return -EINVAL;
+
 #ifdef PPC64_ELF_ABI_v1
 	/* func points to the function descriptor */
 	PPC_LI64(b2p[TMP_REG_2], func);
@@ -157,25 +161,23 @@ static void bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx,
 	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_FUNC_ADDR(12, func);
 	EMIT(PPC_RAW_MTCTR(12));
 #endif
 	EMIT(PPC_RAW_BCTRL());
+
+	return 0;
 }
 
-void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func)
+int bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func)
 {
 	unsigned int i, ctx_idx = ctx->idx;
 
+	if (WARN_ON_ONCE(func && is_module_text_address(func)))
+		return -EINVAL;
+
 	/* Load function address into r12 */
 	PPC_LI64(12, func);
 
@@ -193,19 +195,14 @@ void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 fun
 		EMIT(PPC_RAW_NOP());
 
 #ifdef PPC64_ELF_ABI_v1
-	/*
-	 * 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(12));
 	EMIT(PPC_RAW_BCTRL());
+
+	return 0;
 }
 
 static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 out)
@@ -890,9 +887,13 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 				return ret;
 
 			if (func_addr_fixed)
-				bpf_jit_emit_func_call_hlp(image, ctx, func_addr);
+				ret = bpf_jit_emit_func_call_hlp(image, ctx, func_addr);
 			else
-				bpf_jit_emit_func_call_rel(image, ctx, func_addr);
+				ret = bpf_jit_emit_func_call_rel(image, ctx, func_addr);
+
+			if (ret)
+				return ret;
+
 			/* move return value from r3 to BPF_REG_0 */
 			EMIT(PPC_RAW_MR(b2p[BPF_REG_0], 3));
 			break;