[PATCH 2/9] powerpc/bpf: Validate branch ranges

[Naveen N. Rao]

Add checks to ensure that we never emit branch instructions with
truncated branch offsets.

Suggested-by: Michael Ellerman <mpe at ellerman.id.au>
Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
---
 arch/powerpc/net/bpf_jit.h        | 26 ++++++++++++++++++++------
 arch/powerpc/net/bpf_jit_comp.c   |  6 +++++-
 arch/powerpc/net/bpf_jit_comp32.c |  8 ++++++--
 arch/powerpc/net/bpf_jit_comp64.c |  8 ++++++--
 4 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
index 935ea95b66359e..7e9b978b768ed9 100644
--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -24,16 +24,30 @@
 #define EMIT(instr)		PLANT_INSTR(image, ctx->idx, instr)
 
 /* Long jump; (unconditional 'branch') */
-#define PPC_JMP(dest)		EMIT(PPC_INST_BRANCH |			      \
-				     (((dest) - (ctx->idx * 4)) & 0x03fffffc))
+#define PPC_JMP(dest)							      \
+	do {								      \
+		long offset = (long)(dest) - (ctx->idx * 4);		      \
+		if (!is_offset_in_branch_range(offset)) {		      \
+			pr_err_ratelimited("Branch offset 0x%lx (@%u) out of range\n", offset, ctx->idx);			\
+			return -ERANGE;					      \
+		}							      \
+		EMIT(PPC_INST_BRANCH | (offset & 0x03fffffc));		      \
+	} while (0)
+
 /* blr; (unconditional 'branch' with link) to absolute address */
 #define PPC_BL_ABS(dest)	EMIT(PPC_INST_BL |			      \
 				     (((dest) - (unsigned long)(image + ctx->idx)) & 0x03fffffc))
 /* "cond" here covers BO:BI fields. */
-#define PPC_BCC_SHORT(cond, dest)	EMIT(PPC_INST_BRANCH_COND |	      \
-					     (((cond) & 0x3ff) << 16) |	      \
-					     (((dest) - (ctx->idx * 4)) &     \
-					      0xfffc))
+#define PPC_BCC_SHORT(cond, dest)					      \
+	do {								      \
+		long offset = (long)(dest) - (ctx->idx * 4);		      \
+		if (!is_offset_in_cond_branch_range(offset)) {		      \
+			pr_err_ratelimited("Conditional branch offset 0x%lx (@%u) out of range\n", offset, ctx->idx);		\
+			return -ERANGE;					      \
+		}							      \
+		EMIT(PPC_INST_BRANCH_COND | (((cond) & 0x3ff) << 16) | (offset & 0xfffc));					\
+	} while (0)
+
 /* Sign-extended 32-bit immediate load */
 #define PPC_LI32(d, i)		do {					      \
 		if ((int)(uintptr_t)(i) >= -32768 &&			      \
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 53aefee3fe70be..fcbf7a917c566e 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -210,7 +210,11 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 		/* Now build the prologue, body code & epilogue for real. */
 		cgctx.idx = 0;
 		bpf_jit_build_prologue(code_base, &cgctx);
-		bpf_jit_build_body(fp, code_base, &cgctx, addrs, extra_pass);
+		if (bpf_jit_build_body(fp, code_base, &cgctx, addrs, extra_pass)) {
+			bpf_jit_binary_free(bpf_hdr);
+			fp = org_fp;
+			goto out_addrs;
+		}
 		bpf_jit_build_epilogue(code_base, &cgctx);
 
 		if (bpf_jit_enable > 1)
diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index beb12cbc8c2994..a74d52204f8da2 100644
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -200,7 +200,7 @@ void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 fun
 	}
 }
 
-static void 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)
 {
 	/*
 	 * By now, the eBPF program has already setup parameters in r3-r6
@@ -261,7 +261,9 @@ static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32
 	bpf_jit_emit_common_epilogue(image, ctx);
 
 	EMIT(PPC_RAW_BCTR());
+
 	/* out: */
+	return 0;
 }
 
 /* Assemble the body code between the prologue & epilogue */
@@ -1090,7 +1092,9 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 		 */
 		case BPF_JMP | BPF_TAIL_CALL:
 			ctx->seen |= SEEN_TAILCALL;
-			bpf_jit_emit_tail_call(image, ctx, addrs[i + 1]);
+			ret = bpf_jit_emit_tail_call(image, ctx, addrs[i + 1]);
+			if (ret < 0)
+				return ret;
 			break;
 
 		default:
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index b87a63dba9c8fb..f06c62089b1457 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -206,7 +206,7 @@ void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 fun
 	EMIT(PPC_RAW_BCTRL());
 }
 
-static void 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)
 {
 	/*
 	 * By now, the eBPF program has already setup parameters in r3, r4 and r5
@@ -267,7 +267,9 @@ static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32
 	bpf_jit_emit_common_epilogue(image, ctx);
 
 	EMIT(PPC_RAW_BCTR());
+
 	/* out: */
+	return 0;
 }
 
 /* Assemble the body code between the prologue & epilogue */
@@ -993,7 +995,9 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 		 */
 		case BPF_JMP | BPF_TAIL_CALL:
 			ctx->seen |= SEEN_TAILCALL;
-			bpf_jit_emit_tail_call(image, ctx, addrs[i + 1]);
+			ret = bpf_jit_emit_tail_call(image, ctx, addrs[i + 1]);
+			if (ret < 0)
+				return ret;
 			break;
 
 		default:
-- 
2.33.0