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

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 01/10/2021 à 23:14, Naveen N. Rao a écrit :
> 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>
> ---
>   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);			\

Does it really deserves a KERN_ERR ?
Isn't that something that can trigger with a userland request ?

> +			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);		\

Same

> +			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:
>