From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DCAD6C43334 for ; Mon, 11 Jul 2022 09:26:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232282AbiGKJ0M (ORCPT ); Mon, 11 Jul 2022 05:26:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55050 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232343AbiGKJYb (ORCPT ); Mon, 11 Jul 2022 05:24:31 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8C6C123150; Mon, 11 Jul 2022 02:14:39 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1DEE8610A5; Mon, 11 Jul 2022 09:14:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2B2E2C34115; Mon, 11 Jul 2022 09:14:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1657530878; bh=5D836XQBOGnEC4gj8gALZ38OdTXjtmvc8NRllUhKRfg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GhGveSKxqYVrVCCVlXCVok+w/imsSRJ73vgp51UTf6oc76jaaNVF20sNv/sIETpbW BjkVPLClDgmCEv/tloDxKfB45MYusEn9Kpf2M4NmpJBhV6WUPELVqx3ygKTsFy+dId KouhCG7FFsecDv5+4twy96qLSD0Tu8mDgwK8cBRc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Kuee K1r0a , Daniel Borkmann , Andrii Nakryiko , John Fastabend Subject: [PATCH 5.18 017/112] bpf: Fix insufficient bounds propagation from adjust_scalar_min_max_vals Date: Mon, 11 Jul 2022 11:06:17 +0200 Message-Id: <20220711090550.048634501@linuxfoundation.org> X-Mailer: git-send-email 2.37.0 In-Reply-To: <20220711090549.543317027@linuxfoundation.org> References: <20220711090549.543317027@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Daniel Borkmann commit 3844d153a41adea718202c10ae91dc96b37453b5 upstream. Kuee reported a corner case where the tnum becomes constant after the call to __reg_bound_offset(), but the register's bounds are not, that is, its min bounds are still not equal to the register's max bounds. This in turn allows to leak pointers through turning a pointer register as is into an unknown scalar via adjust_ptr_min_max_vals(). Before: func#0 @0 0: R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 0: (b7) r0 = 1 ; R0_w=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) 1: (b7) r3 = 0 ; R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0)) 2: (87) r3 = -r3 ; R3_w=scalar() 3: (87) r3 = -r3 ; R3_w=scalar() 4: (47) r3 |= 32767 ; R3_w=scalar(smin=-9223372036854743041,umin=32767,var_off=(0x7fff; 0xffffffffffff8000),s32_min=-2147450881) 5: (75) if r3 s>= 0x0 goto pc+1 ; R3_w=scalar(umin=9223372036854808575,var_off=(0x8000000000007fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767) 6: (95) exit from 5 to 7: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 7: (d5) if r3 s<= 0x8000 goto pc+1 ; R3=scalar(umin=32769,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767) 8: (95) exit from 7 to 9: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=32768,var_off=(0x7fff; 0x8000)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 9: (07) r3 += -32767 ; R3_w=scalar(imm=0,umax=1,var_off=(0x0; 0x0)) <--- [*] 10: (95) exit What can be seen here is that R3=scalar(umin=32767,umax=32768,var_off=(0x7fff; 0x8000)) after the operation R3 += -32767 results in a 'malformed' constant, that is, R3_w=scalar(imm=0,umax=1,var_off=(0x0; 0x0)). Intersecting with var_off has not been done at that point via __update_reg_bounds(), which would have improved the umax to be equal to umin. Refactor the tnum <> min/max bounds information flow into a reg_bounds_sync() helper and use it consistently everywhere. After the fix, bounds have been corrected to R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0)) and thus the register is regarded as a 'proper' constant scalar of 0. After: func#0 @0 0: R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 0: (b7) r0 = 1 ; R0_w=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) 1: (b7) r3 = 0 ; R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0)) 2: (87) r3 = -r3 ; R3_w=scalar() 3: (87) r3 = -r3 ; R3_w=scalar() 4: (47) r3 |= 32767 ; R3_w=scalar(smin=-9223372036854743041,umin=32767,var_off=(0x7fff; 0xffffffffffff8000),s32_min=-2147450881) 5: (75) if r3 s>= 0x0 goto pc+1 ; R3_w=scalar(umin=9223372036854808575,var_off=(0x8000000000007fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767) 6: (95) exit from 5 to 7: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 7: (d5) if r3 s<= 0x8000 goto pc+1 ; R3=scalar(umin=32769,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767) 8: (95) exit from 7 to 9: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=32768,var_off=(0x7fff; 0x8000)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 9: (07) r3 += -32767 ; R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0)) <--- [*] 10: (95) exit Fixes: b03c9f9fdc37 ("bpf/verifier: track signed and unsigned min/max values") Reported-by: Kuee K1r0a Signed-off-by: Daniel Borkmann Signed-off-by: Andrii Nakryiko Acked-by: John Fastabend Link: https://lore.kernel.org/bpf/20220701124727.11153-2-daniel@iogearbox.net Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/verifier.c | 72 +++++++++++++++----------------------------------- 1 file changed, 23 insertions(+), 49 deletions(-) --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1417,6 +1417,21 @@ static void __reg_bound_offset(struct bp reg->var_off = tnum_or(tnum_clear_subreg(var64_off), var32_off); } +static void reg_bounds_sync(struct bpf_reg_state *reg) +{ + /* We might have learned new bounds from the var_off. */ + __update_reg_bounds(reg); + /* We might have learned something about the sign bit. */ + __reg_deduce_bounds(reg); + /* We might have learned some bits from the bounds. */ + __reg_bound_offset(reg); + /* Intersecting with the old var_off might have improved our bounds + * slightly, e.g. if umax was 0x7f...f and var_off was (0; 0xf...fc), + * then new var_off is (0; 0x7f...fc) which improves our umax. + */ + __update_reg_bounds(reg); +} + static bool __reg32_bound_s64(s32 a) { return a >= 0 && a <= S32_MAX; @@ -1458,16 +1473,8 @@ static void __reg_combine_32_into_64(str * so they do not impact tnum bounds calculation. */ __mark_reg64_unbounded(reg); - __update_reg_bounds(reg); } - - /* Intersecting with the old var_off might have improved our bounds - * slightly. e.g. if umax was 0x7f...f and var_off was (0; 0xf...fc), - * then new var_off is (0; 0x7f...fc) which improves our umax. - */ - __reg_deduce_bounds(reg); - __reg_bound_offset(reg); - __update_reg_bounds(reg); + reg_bounds_sync(reg); } static bool __reg64_bound_s32(s64 a) @@ -1483,7 +1490,6 @@ static bool __reg64_bound_u32(u64 a) static void __reg_combine_64_into_32(struct bpf_reg_state *reg) { __mark_reg32_unbounded(reg); - if (__reg64_bound_s32(reg->smin_value) && __reg64_bound_s32(reg->smax_value)) { reg->s32_min_value = (s32)reg->smin_value; reg->s32_max_value = (s32)reg->smax_value; @@ -1492,14 +1498,7 @@ static void __reg_combine_64_into_32(str reg->u32_min_value = (u32)reg->umin_value; reg->u32_max_value = (u32)reg->umax_value; } - - /* Intersecting with the old var_off might have improved our bounds - * slightly. e.g. if umax was 0x7f...f and var_off was (0; 0xf...fc), - * then new var_off is (0; 0x7f...fc) which improves our umax. - */ - __reg_deduce_bounds(reg); - __reg_bound_offset(reg); - __update_reg_bounds(reg); + reg_bounds_sync(reg); } /* Mark a register as having a completely unknown (scalar) value. */ @@ -6485,9 +6484,7 @@ static void do_refine_retval_range(struc ret_reg->s32_max_value = meta->msize_max_value; ret_reg->smin_value = -MAX_ERRNO; ret_reg->s32_min_value = -MAX_ERRNO; - __reg_deduce_bounds(ret_reg); - __reg_bound_offset(ret_reg); - __update_reg_bounds(ret_reg); + reg_bounds_sync(ret_reg); } static int @@ -7693,11 +7690,7 @@ static int adjust_ptr_min_max_vals(struc if (!check_reg_sane_offset(env, dst_reg, ptr_reg->type)) return -EINVAL; - - __update_reg_bounds(dst_reg); - __reg_deduce_bounds(dst_reg); - __reg_bound_offset(dst_reg); - + reg_bounds_sync(dst_reg); if (sanitize_check_bounds(env, insn, dst_reg) < 0) return -EACCES; if (sanitize_needed(opcode)) { @@ -8435,10 +8428,7 @@ static int adjust_scalar_min_max_vals(st /* ALU32 ops are zero extended into 64bit register */ if (alu32) zext_32_to_64(dst_reg); - - __update_reg_bounds(dst_reg); - __reg_deduce_bounds(dst_reg); - __reg_bound_offset(dst_reg); + reg_bounds_sync(dst_reg); return 0; } @@ -8627,10 +8617,7 @@ static int check_alu_op(struct bpf_verif insn->dst_reg); } zext_32_to_64(dst_reg); - - __update_reg_bounds(dst_reg); - __reg_deduce_bounds(dst_reg); - __reg_bound_offset(dst_reg); + reg_bounds_sync(dst_reg); } } else { /* case: R = imm @@ -9233,21 +9220,8 @@ static void __reg_combine_min_max(struct dst_reg->smax_value); src_reg->var_off = dst_reg->var_off = tnum_intersect(src_reg->var_off, dst_reg->var_off); - /* We might have learned new bounds from the var_off. */ - __update_reg_bounds(src_reg); - __update_reg_bounds(dst_reg); - /* We might have learned something about the sign bit. */ - __reg_deduce_bounds(src_reg); - __reg_deduce_bounds(dst_reg); - /* We might have learned some bits from the bounds. */ - __reg_bound_offset(src_reg); - __reg_bound_offset(dst_reg); - /* Intersecting with the old var_off might have improved our bounds - * slightly. e.g. if umax was 0x7f...f and var_off was (0; 0xf...fc), - * then new var_off is (0; 0x7f...fc) which improves our umax. - */ - __update_reg_bounds(src_reg); - __update_reg_bounds(dst_reg); + reg_bounds_sync(src_reg); + reg_bounds_sync(dst_reg); } static void reg_combine_min_max(struct bpf_reg_state *true_src,