[PATCH 4.9 154/207] powerpc/bpf: Validate branch ranges

Greg Kroah-Hartman
2021-11-24T12:23:07Z

From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>

upstream commit 3832ba4e283d7052b783dab8311df7e3590fed93

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

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Tested-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/71d33a6b7603ec1013c9734dd8bdd4ff5e929142.1633464148.git.naveen.n.rao@linux.vnet.ibm.com
[expand is_offset_in_[cond_]branch_range() helpers, drop ppc32 changes]
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/net/bpf_jit.h | 25 +++++++++++++++++++------
arch/powerpc/net/bpf_jit_comp64.c | 10 +++++++---
2 files changed, 26 insertions(+), 9 deletions(-)

--- a/arch/powerpc/net/bpf_jit.h
+++ b/arch/powerpc/net/bpf_jit.h
@@ -177,13 +177,26 @@
#define PPC_NEG(d, a) EMIT(PPC_INST_NEG | ___PPC_RT(d) | ___PPC_RA(a))

/* 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 (offset < -0x2000000 || offset > 0x1fffffc || offset & 0x3) { \
+ 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)
/* "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 (offset < -0x8000 || offset > 0x7fff || offset & 0x3) { \
+ 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 && \
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -239,7 +239,7 @@ static void bpf_jit_emit_func_call(u32 *
PPC_BLRL();
}

-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
@@ -300,7 +300,9 @@ static void bpf_jit_emit_tail_call(u32 *
bpf_jit_emit_common_epilogue(image, ctx);

PPC_BCTR();
+
/* out: */
+ return 0;
}

/* Assemble the body code between the prologue & epilogue */
@@ -310,7 +312,7 @@ static int bpf_jit_build_body(struct bpf
{
const struct bpf_insn *insn = fp->insnsi;
int flen = fp->len;
- int i;
+ int i, ret;

/* Start of epilogue code - will only be valid 2nd pass onwards */
u32 exit_addr = addrs[flen];
@@ -938,7 +940,9 @@ common_load:
*/
case BPF_JMP | BPF_CALL | BPF_X:
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;