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From: LEROY Christophe <christophe.leroy@csgroup.eu>
To: Hari Bathini <hbathini@linux.ibm.com>,
	"naveen.n.rao@linux.ibm.com" <naveen.n.rao@linux.ibm.com>,
	"mpe@ellerman.id.au" <mpe@ellerman.id.au>,
	"ast@kernel.org" <ast@kernel.org>,
	"daniel@iogearbox.net" <daniel@iogearbox.net>
Cc: "paulus@samba.org" <paulus@samba.org>,
	"andrii@kernel.org" <andrii@kernel.org>,
	"kafai@fb.com" <kafai@fb.com>,
	"songliubraving@fb.com" <songliubraving@fb.com>,
	"yhs@fb.com" <yhs@fb.com>,
	"john.fastabend@gmail.com" <john.fastabend@gmail.com>,
	"kpsingh@kernel.org" <kpsingh@kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Subject: Re: [PATCH v4 6/8] bpf ppc64: Access only if addr is kernel address
Date: Wed, 29 Sep 2021 11:44:37 +0000	[thread overview]
Message-ID: <dac0a043-51f0-24ba-b9fb-6cf53e4ce15f@csgroup.eu> (raw)
In-Reply-To: <20210929111855.50254-7-hbathini@linux.ibm.com>



Le 29/09/2021 à 13:18, Hari Bathini a écrit :
> From: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
> 
> On PPC64 with KUAP enabled, any kernel code which wants to
> access userspace needs to be surrounded by disable-enable KUAP.
> But that is not happening for BPF_PROBE_MEM load instruction.
> So, when BPF program tries to access invalid userspace address,
> page-fault handler considers it as bad KUAP fault:
> 
>    Kernel attempted to read user page (d0000000) - exploit attempt? (uid: 0)
> 
> Considering the fact that PTR_TO_BTF_ID (which uses BPF_PROBE_MEM
> mode) could either be a valid kernel pointer or NULL but should
> never be a pointer to userspace address, execute BPF_PROBE_MEM load
> only if addr is kernel address, otherwise set dst_reg=0 and move on.
> 
> This will catch NULL, valid or invalid userspace pointers. Only bad
> kernel pointer will be handled by BPF exception table.
> 
> [Alexei suggested for x86]
> Suggested-by: Alexei Starovoitov <ast@kernel.org>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>

> ---
> 
> Changes in v4:
> * Used IS_ENABLED() instead of #ifdef.
> * Dropped the else case that is not applicable for PPC64.
> 
> 
>   arch/powerpc/net/bpf_jit_comp64.c | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 4170999371ee..e1ea64081ae1 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -727,6 +727,32 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
>   		/* dst = *(u64 *)(ul) (src + off) */
>   		case BPF_LDX | BPF_MEM | BPF_DW:
>   		case BPF_LDX | BPF_PROBE_MEM | BPF_DW:
> +			/*
> +			 * As PTR_TO_BTF_ID that uses BPF_PROBE_MEM mode could either be a valid
> +			 * kernel pointer or NULL but not a userspace address, execute BPF_PROBE_MEM
> +			 * load only if addr is kernel address (see is_kernel_addr()), otherwise
> +			 * set dst_reg=0 and move on.
> +			 */
> +			if (BPF_MODE(code) == BPF_PROBE_MEM) {
> +				EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], src_reg, off));
> +				if (IS_ENABLED(CONFIG_PPC_BOOK3E_64))
> +					PPC_LI64(b2p[TMP_REG_2], 0x8000000000000000ul);
> +				else /* BOOK3S_64 */
> +					PPC_LI64(b2p[TMP_REG_2], PAGE_OFFSET);
> +				EMIT(PPC_RAW_CMPLD(b2p[TMP_REG_1], b2p[TMP_REG_2]));
> +				PPC_BCC(COND_GT, (ctx->idx + 4) * 4);
> +				EMIT(PPC_RAW_LI(dst_reg, 0));
> +				/*
> +				 * Check if 'off' is word aligned because PPC_BPF_LL()
> +				 * (BPF_DW case) generates two instructions if 'off' is not
> +				 * word-aligned and one instruction otherwise.
> +				 */
> +				if (BPF_SIZE(code) == BPF_DW && (off & 3))
> +					PPC_JMP((ctx->idx + 3) * 4);
> +				else
> +					PPC_JMP((ctx->idx + 2) * 4);
> +			}
> +
>   			switch (size) {
>   			case BPF_B:
>   				EMIT(PPC_RAW_LBZ(dst_reg, src_reg, off));
> 

  reply	other threads:[~2021-09-29 11:44 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29 11:18 [PATCH v4 0/8] bpf powerpc: Add BPF_PROBE_MEM support in powerpc JIT compiler Hari Bathini
2021-09-29 11:18 ` [PATCH v4 1/8] bpf powerpc: Remove unused SEEN_STACK Hari Bathini
2021-09-29 11:18 ` [PATCH v4 2/8] bpf powerpc: Remove extra_pass from bpf_jit_build_body() Hari Bathini
2021-09-29 11:18 ` [PATCH v4 3/8] bpf powerpc: refactor JIT compiler code Hari Bathini
2021-09-29 11:42   ` Christophe Leroy
2021-09-29 11:18 ` [PATCH v4 4/8] powerpc/ppc-opcode: introduce PPC_RAW_BRANCH() macro Hari Bathini
2021-09-29 11:18 ` [PATCH v4 5/8] bpf ppc64: Add BPF_PROBE_MEM support for JIT Hari Bathini
2021-09-29 11:43   ` Christophe Leroy
2021-09-29 11:47   ` Christophe Leroy
2021-09-30  4:18     ` Jordan Niethe
2021-09-29 11:18 ` [PATCH v4 6/8] bpf ppc64: Access only if addr is kernel address Hari Bathini
2021-09-29 11:44   ` LEROY Christophe [this message]
2021-09-29 11:18 ` [PATCH v4 7/8] bpf ppc32: Add BPF_PROBE_MEM support for JIT Hari Bathini
2021-09-29 11:44   ` Christophe Leroy
2021-09-29 11:18 ` [PATCH v4 8/8] bpf ppc32: Access only if addr is kernel address Hari Bathini
2021-09-29 11:45   ` Christophe Leroy
2021-09-30 20:57 ` [PATCH v4 0/8] bpf powerpc: Add BPF_PROBE_MEM support in powerpc JIT compiler Daniel Borkmann
2021-10-01 21:22   ` Naveen N. Rao
2021-10-03 22:49   ` Michael Ellerman
2021-10-04  8:05     ` Daniel Borkmann
2021-10-04  8:43       ` Michael Ellerman

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