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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id h11-20020a17090634cb00b00a0f770ae91bsm5692884ejb.89.2023.12.04.14.12.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Dec 2023 14:12:31 -0800 (PST) Message-ID: <3fca38fdfd975f735e3dd31930637cfbc70948f4.camel@gmail.com> Subject: Re: [PATCH v3 bpf-next 03/10] bpf: fix check for attempt to corrupt spilled pointer From: Eduard Zingerman To: Andrii Nakryiko , bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, martin.lau@kernel.org Cc: kernel-team@meta.com Date: Tue, 05 Dec 2023 00:12:30 +0200 In-Reply-To: <20231204192601.2672497-4-andrii@kernel.org> References: <20231204192601.2672497-1-andrii@kernel.org> <20231204192601.2672497-4-andrii@kernel.org> Autocrypt: addr=eddyz87@gmail.com; prefer-encrypt=mutual; keydata=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 nYzhLWGcczc6J71q1Dje0l5vIPaSFOgwmWD4DA+WvuxM/shH4rtWeodbv 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 t1iq+gsfnXbPz5AnS598ScZI1oP7OrPSFJkt/z4acEbOQDQs8aUqrd46PV jsdqGvKnXZxzylux29UTNby4jTlz9pNJM+wPrDRmGfchLDUmf6CffaUYCbu4FiId+9+dcTCDvxbABRy1C3OJ8QY7cxfJ+pEZW18fRJ0XCl/fiV/ecAOfB3HsqgTzAn555h0rkFgay0hAvMU/mAW/CFNSIxV397zm749ZNLA0L2dMy1AKuOqH+/B+/ImBfJMDjmdyJQ8WU/OFRuGLdqOd2oZrA1iuPIa+yUYyZkaZfz/emQwpIL1+Q4p1R/OplA4yc301AqruXXUcVDbEB+joHW3hy5FwK5t5OwTKatrSJBkydSF9zdXy98fYzGniRyRA65P0Ix/8J3BYB4edY2/w0Ip/mdYsYQljBY0A== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.1 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2023-12-04 at 11:25 -0800, Andrii Nakryiko wrote: [...] > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 4f8a3c77eb80..73315e2f20d9 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -4431,7 +4431,7 @@ static int check_stack_write_fixed_off(struct bpf_v= erifier_env *env, > * so it's aligned access and [off, off + size) are within stack limits > */ > if (!env->allow_ptr_leaks && > - state->stack[spi].slot_type[0] =3D=3D STACK_SPILL && > + is_spilled_reg(&state->stack[spi]) && > size !=3D BPF_REG_SIZE) { > verbose(env, "attempt to corrupt spilled pointer on stack\n"); > return -EACCES; I think there is a small detail here. slot_type[0] =3D=3D STACK_SPILL actually checks if a spill is 64-bit. Thus, with this patch applied the test below does not pass. Log fragment: 1: (57) r0 &=3D 65535 ; R0_w=3Dscalar(...,var_off=3D(= 0x0; 0xffff)) 2: (63) *(u32 *)(r10 -8) =3D r0 3: R0_w=3Dscalar(...,var_off=3D(0x0; 0xffff)) R10=3Dfp0 fp-8=3Dmmmmscal= ar(...,var_off=3D(0x0; 0xffff)) 3: (b7) r0 =3D 42 ; R0_w=3D42 4: (63) *(u32 *)(r10 -4) =3D r0 attempt to corrupt spilled pointer on stack Admittedly, this happens only when the only capability is CAP_BPF and we don't test this configuration. --- iff --git a/tools/testing/selftests/bpf/progs/verifier_basic_stack.c b/tool= s/testing/selftests/bpf/progs/verifier_basic_stack.c index 359df865a8f3..61ada86e84df 100644 --- a/tools/testing/selftests/bpf/progs/verifier_basic_stack.c +++ b/tools/testing/selftests/bpf/progs/verifier_basic_stack.c @@ -97,4 +97,20 @@ __naked void misaligned_read_from_stack(void) " ::: __clobber_all); } =20 +SEC("socket") +__success_unpriv +__naked void spill_lo32_write_hi32(void) +{ + asm volatile (" \ + call %[bpf_get_prandom_u32]; \ + r0 &=3D 0xffff; \ + *(u32*)(r10 - 8) =3D r0; \ + r0 =3D 42; \ + *(u32*)(r10 - 4) =3D r0; \ + exit; \ +" : + : __imm(bpf_get_prandom_u32) + : __clobber_all); +} + char _license[] SEC("license") =3D "GPL"; diff --git a/tools/testing/selftests/bpf/test_loader.c b/tools/testing/self= tests/bpf/test_loader.c index a350ecdfba4a..a5ad6b01175e 100644 --- a/tools/testing/selftests/bpf/test_loader.c +++ b/tools/testing/selftests/bpf/test_loader.c @@ -430,7 +430,7 @@ struct cap_state { static int drop_capabilities(struct cap_state *caps) { const __u64 caps_to_drop =3D (1ULL << CAP_SYS_ADMIN | 1ULL << CAP_N= ET_ADMIN | - 1ULL << CAP_PERFMON | 1ULL << CAP_BPF= ); + 1ULL << CAP_PERFMON /*| 1ULL << CAP_BPF= */); int err; =20 err =3D cap_disable_effective(caps_to_drop, &caps->old_caps);