From patchwork Wed Dec 6 16:58:01 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrei Matei X-Patchwork-Id: 13482044 X-Patchwork-Delegate: bpf@iogearbox.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="BEe1/TY2" Received: from mail-oo1-xc32.google.com (mail-oo1-xc32.google.com [IPv6:2607:f8b0:4864:20::c32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 819A1D3 for ; Wed, 6 Dec 2023 08:58:45 -0800 (PST) Received: by mail-oo1-xc32.google.com with SMTP id 006d021491bc7-58db7d8f2ebso4610769eaf.0 for ; Wed, 06 Dec 2023 08:58:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1701881924; x=1702486724; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=SFNY4aAGR7NerwCwtVfqRbMoEy7iMW2l2HbBMz/O8hY=; b=BEe1/TY2zonzSMDtF6mXCy9/f3yITt9OGCiQrH1bwBlC1QUCsFSfgtwa4t0s5xKvry CD6/2oOb8lqWYMLSHT8e3kzWeYPSfOS036xXA/o9gi9Ke8qRF1o4dyxXBM4XV9hRiz4l v2C9qpR7PQNs0IdzsRzOcGyScphIJ6qbFLZLi31T9dxAI5uj9vSRdMu8ltBQZTGMdSOX e1hXibdb4TiwfZLE4rZZsjMOT6CGwySYP60SNHbUOtvfCyembKYX5IU7DHJsHOkJMr+s 1R19g2M4rkdrSO6SNygJn6eF2utK5eDZxbKP7XrXci21jatV7in0/SushPZ8yqcJhyde wpSQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701881924; x=1702486724; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=SFNY4aAGR7NerwCwtVfqRbMoEy7iMW2l2HbBMz/O8hY=; b=nWhzRRg6RDJ03plU3yaPkIrNHTtwW1MmjNpCzTsrlqzKwAbpdGQ3+Y1pddOkWSscHL mCEkBv7c3ZR619Usp73shSmQI+5nOs8ZwozhmokG9ij2psdQ7GMCxFI5DDZ5x1t0OPB/ /KaP0lRpU/YvME5Jf/ylHUJl/A0l9ReM+MiVleMy7V+utt5sRmNDgZ7hXUB543gsvhk/ Za9dmgoQ0GpSeTpG+OnPEk+qQcIK5KIESq7YTsfs/+rh/ScH51SA6WyT5HpaN4BBqNHO Nave6qC7Nn4OyvEcfPBEIo2y7w2i0OJdkKKYHFmxFl71N0MTcb1dYYJnONPNGnbXGHoz HxQw== X-Gm-Message-State: AOJu0YxcKDUP/CVx4ZGfaDDYW4HvHGkHHKUDQhKTI5wMZqTPr7Mbh3ot 739EJhQuCGwa/3tjxQUiKN0HKtGpQh8= X-Google-Smtp-Source: AGHT+IHImopTMdgGMfvnvT3saTSLrJYtWJeSzrFaghAFUADUdjT5XE6i0ePHDQSvWEdv4e8BkBKrXA== X-Received: by 2002:a05:6358:5922:b0:16b:f950:3d83 with SMTP id g34-20020a056358592200b0016bf9503d83mr1568712rwf.31.1701881923647; Wed, 06 Dec 2023 08:58:43 -0800 (PST) Received: from andrei-desktop.taildd130.ts.net ([71.125.252.241]) by smtp.gmail.com with ESMTPSA id h17-20020a0cf8d1000000b0067a3991d002sm118372qvo.30.2023.12.06.08.58.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Dec 2023 08:58:43 -0800 (PST) From: Andrei Matei To: bpf@vger.kernel.org, andrii.nakryiko@gmail.com, sunhao.th@gmail.com, eddyz87@gmail.com Cc: Andrei Matei Subject: [PATCH bpf-next v4 1/2] bpf: fix verification of indirect var-off stack access Date: Wed, 6 Dec 2023 11:58:01 -0500 Message-Id: <20231206165802.380626-2-andreimatei1@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20231206165802.380626-1-andreimatei1@gmail.com> References: <20231206165802.380626-1-andreimatei1@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net This patch fixes a bug around the verification of possibly-zero-sized stack accesses. When the access was done through a var-offset stack pointer, check_stack_access_within_bounds was incorrectly computing the maximum-offset of a zero-sized read to be the same as the register's min offset. Instead, we have to take in account the register's maximum possible value. The patch also simplifies how the max offset is checked; the check is now simpler than for min offset. The bug was allowing accesses to erroneously pass the check_stack_access_within_bounds() checks, only to later crash in check_stack_range_initialized() when all the possibly-affected stack slots are iterated (this time with a correct max offset). check_stack_range_initialized() is relying on check_stack_access_within_bounds() for its accesses to the stack-tracking vector to be within bounds; in the case of zero-sized accesses, we were essentially only verifying that the lowest possible slot was within bounds. We would crash when the max-offset of the stack pointer was >= 0 (which shouldn't pass verification, and hopefully is not something anyone's code attempts to do in practice). Thanks Hao for reporting! Reported-by: Hao Sun Fixes: 01f810ace9ed3 ("bpf: Allow variable-offset stack access") Closes: https://lore.kernel.org/bpf/CACkBjsZGEUaRCHsmaX=h-efVogsRfK1FPxmkgb0Os_frnHiNdw@mail.gmail.com/ Signed-off-by: Andrei Matei Acked-by: Andrii Nakryiko --- kernel/bpf/verifier.c | 14 +++------ .../selftests/bpf/progs/verifier_var_off.c | 29 +++++++++++++++++++ 2 files changed, 33 insertions(+), 10 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index e5ce530641ba..137240681fa9 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6620,10 +6620,7 @@ static int check_stack_access_within_bounds( if (tnum_is_const(reg->var_off)) { min_off = reg->var_off.value + off; - if (access_size > 0) - max_off = min_off + access_size - 1; - else - max_off = min_off; + max_off = min_off + access_size; } else { if (reg->smax_value >= BPF_MAX_VAR_OFF || reg->smin_value <= -BPF_MAX_VAR_OFF) { @@ -6632,15 +6629,12 @@ static int check_stack_access_within_bounds( return -EACCES; } min_off = reg->smin_value + off; - if (access_size > 0) - max_off = reg->smax_value + off + access_size - 1; - else - max_off = min_off; + max_off = reg->smax_value + off + access_size; } err = check_stack_slot_within_bounds(min_off, state, type); - if (!err) - err = check_stack_slot_within_bounds(max_off, state, type); + if (!err && max_off > 0) + err = -EINVAL; /* out of stack access into non-negative offsets */ if (err) { if (tnum_is_const(reg->var_off)) { diff --git a/tools/testing/selftests/bpf/progs/verifier_var_off.c b/tools/testing/selftests/bpf/progs/verifier_var_off.c index 83a90afba785..9fb32b292017 100644 --- a/tools/testing/selftests/bpf/progs/verifier_var_off.c +++ b/tools/testing/selftests/bpf/progs/verifier_var_off.c @@ -224,6 +224,35 @@ __naked void access_max_out_of_bound(void) : __clobber_all); } +/* Similar to the test above, but this time check the special case of a + * zero-sized stack access. We used to have a bug causing crashes for zero-sized + * out-of-bounds accesses. + */ +SEC("socket") +__description("indirect variable-offset stack access, zero-sized, max out of bound") +__failure __msg("invalid variable-offset indirect access to stack R1") +__naked void zero_sized_access_max_out_of_bound(void) +{ + asm volatile (" \ + r0 = 0; \ + /* Fill some stack */ \ + *(u64*)(r10 - 16) = r0; \ + *(u64*)(r10 - 8) = r0; \ + /* Get an unknown value */ \ + r1 = *(u32*)(r1 + 0); \ + r1 &= 64; \ + r1 += -16; \ + /* r1 is now anywhere in [-16,48)*/ \ + r1 += r10; \ + r2 = 0; \ + r3 = 0; \ + call %[bpf_probe_read_kernel]; \ + exit; \ +" : + : __imm(bpf_probe_read_kernel) + : __clobber_all); +} + SEC("lwt_in") __description("indirect variable-offset stack access, min out of bound") __failure __msg("invalid variable-offset indirect access to stack R2") From patchwork Wed Dec 6 16:58:02 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrei Matei X-Patchwork-Id: 13482045 X-Patchwork-Delegate: bpf@iogearbox.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="SHqO+nln" Received: from mail-qv1-xf2b.google.com (mail-qv1-xf2b.google.com [IPv6:2607:f8b0:4864:20::f2b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3E0F4C9 for ; Wed, 6 Dec 2023 08:58:54 -0800 (PST) Received: by mail-qv1-xf2b.google.com with SMTP id 6a1803df08f44-67abd1879c0so94636d6.2 for ; Wed, 06 Dec 2023 08:58:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1701881932; x=1702486732; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=UzyvyDf0ksVmv0SY+k418p2u/uDCxEL3YpuEDFTHZl0=; b=SHqO+nlnxjP0N9m8J9w3kfrAImjGK35nlya3cW5eyejVijqx1uV8OVcf+bBuqBCW2G Rv07gFmjiPtlM9+2hlRTuq/ow7NRYJ06Fadx6M04aDQrO+O9ppaNQNvXDRNBJz116IW3 I8R3yyGMVlyto/PrAouphkFeQCG6QzdC+fUWkq5etxvb1eBZVeFG6Mho6o22Yh9nMqOO QGU06XWuadoripfzKR1O0+Tq3RMblcBy1Kl6mFUKDynpouOkMHV2q5oDdO+gjj2IYpOU fAYPbUkTeLi3s7d27yEaF9Z+6yT3F1zN6cIyHVP0wnmkq3q3GTCOSJf3ZO8tEmDdd0Xv GWLA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701881932; x=1702486732; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=UzyvyDf0ksVmv0SY+k418p2u/uDCxEL3YpuEDFTHZl0=; b=ewCu2MQaC+5pyTTwG+R6I3mj3gk1cH9+o23/TVHTKpPEq9IFCksl6dLiooa3qpMyb4 Qrc4UfNOaVadzcilNrczgjsNM22Y97S6FBtE7Lf93xnsSpbakmBX+QRODAZShyWKnMAp DLZ4PFjwd+jPfsQuk2IEwctNS8zEO63+f8H+t+i96+vAvYGZkht1gwVqtlOZ5HQR3LTJ a1Ef5iBOVRF95I3dT+fRVuAU59NO+ePo/0GuLS5qx4LJ21JxbZ6BnH7sVsKuWBI5fzyK wHhHIJCfkIUi5y41B2CBjCmeuz913P339FDS2FbcxvS+Zq06wEeXwPPu0j+k4lTARHmQ tH0Q== X-Gm-Message-State: AOJu0YxJFl6XdzQ+33Je5rJXEHs3sCUg4EkBI8eUfXzMx2IK0Iivay/c yaYC5T/Fr8nmdMVXkK0p9Tpk4ZTRefM= X-Google-Smtp-Source: AGHT+IHDEw+ystozyIU6z3FWYhKxznGl1amtkJkfU83K7E7M5pZMV1qZ24T6/aMOXGoQ2y4FOpN0fA== X-Received: by 2002:ad4:4eae:0:b0:67a:c40f:fc1b with SMTP id ed14-20020ad44eae000000b0067ac40ffc1bmr1339739qvb.96.1701881932415; Wed, 06 Dec 2023 08:58:52 -0800 (PST) Received: from andrei-desktop.taildd130.ts.net ([71.125.252.241]) by smtp.gmail.com with ESMTPSA id h17-20020a0cf8d1000000b0067a3991d002sm118372qvo.30.2023.12.06.08.58.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Dec 2023 08:58:52 -0800 (PST) From: Andrei Matei To: bpf@vger.kernel.org, andrii.nakryiko@gmail.com, sunhao.th@gmail.com, eddyz87@gmail.com Cc: Andrei Matei Subject: [PATCH bpf-next v4 2/2] bpf: guard stack limits against 32bit overflow Date: Wed, 6 Dec 2023 11:58:02 -0500 Message-Id: <20231206165802.380626-3-andreimatei1@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20231206165802.380626-1-andreimatei1@gmail.com> References: <20231206165802.380626-1-andreimatei1@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net This patch promotes the arithmetic around checking stack bounds to be done in the 64-bit domain, instead of the current 32bit. The arithmetic implies adding together a 64-bit register with a int offset. The register was checked to be below 1<<29 when it was variable, but not when it was fixed. The offset either comes from an instruction (in which case it is 16 bit), from another register (in which case the caller checked it to be below 1<<29 [1]), or from the size of an argument to a kfunc (in which case it can be a u32 [2]). Between the register being inconsistently checked to be below 1<<29, and the offset being up to an u32, it appears that we were open to overflowing the `int`s which were currently used for arithmetic. [1] https://github.com/torvalds/linux/blob/815fb87b753055df2d9e50f6cd80eb10235fe3e9/kernel/bpf/verifier.c#L7494-L7498 [2] https://github.com/torvalds/linux/blob/815fb87b753055df2d9e50f6cd80eb10235fe3e9/kernel/bpf/verifier.c#L11904 Signed-off-by: Andrei Matei Reported-by: Andrii Nakryiko Acked-by: Andrii Nakryiko --- kernel/bpf/verifier.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 137240681fa9..6832ed743765 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6577,7 +6577,7 @@ static int check_ptr_to_map_access(struct bpf_verifier_env *env, * The minimum valid offset is -MAX_BPF_STACK for writes, and * -state->allocated_stack for reads. */ -static int check_stack_slot_within_bounds(int off, +static int check_stack_slot_within_bounds(s64 off, struct bpf_func_state *state, enum bpf_access_type t) { @@ -6606,7 +6606,7 @@ static int check_stack_access_within_bounds( struct bpf_reg_state *regs = cur_regs(env); struct bpf_reg_state *reg = regs + regno; struct bpf_func_state *state = func(env, reg); - int min_off, max_off; + s64 min_off, max_off; int err; char *err_extra; @@ -6619,7 +6619,7 @@ static int check_stack_access_within_bounds( err_extra = " write to"; if (tnum_is_const(reg->var_off)) { - min_off = reg->var_off.value + off; + min_off = (s64)reg->var_off.value + off; max_off = min_off + access_size; } else { if (reg->smax_value >= BPF_MAX_VAR_OFF ||