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From: Hari Bathini <hbathini@linux.ibm.com>
To: naveen.n.rao@linux.ibm.com, christophe.leroy@csgroup.eu,
	mpe@ellerman.id.au, ast@kernel.org, daniel@iogearbox.net
Cc: paulus@samba.org, andrii@kernel.org, kafai@fb.com,
	songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com,
	kpsingh@kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org,
	Hari Bathini <hbathini@linux.ibm.com>
Subject: [PATCH v4 8/8] bpf ppc32: Access only if addr is kernel address
Date: Wed, 29 Sep 2021 16:48:55 +0530	[thread overview]
Message-ID: <20210929111855.50254-9-hbathini@linux.ibm.com> (raw)
In-Reply-To: <20210929111855.50254-1-hbathini@linux.ibm.com>

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. Though PPC32 does not
support read protection, 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: Hari Bathini <hbathini@linux.ibm.com>
---

Changes in v4:
* Adjusted the emit code to avoid using temporary reg.


 arch/powerpc/net/bpf_jit_comp32.c | 34 +++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index 6ee13a09c70d..2ac81563c78d 100644
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -818,6 +818,40 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 		case BPF_LDX | BPF_PROBE_MEM | BPF_W:
 		case BPF_LDX | BPF_MEM | BPF_DW: /* dst = *(u64 *)(ul) (src + off) */
 		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) {
+				PPC_LI32(_R0, TASK_SIZE - off);
+				EMIT(PPC_RAW_CMPLW(src_reg, _R0));
+				PPC_BCC(COND_GT, (ctx->idx + 5) * 4);
+				EMIT(PPC_RAW_LI(dst_reg, 0));
+				/*
+				 * For BPF_DW case, "li reg_h,0" would be needed when
+				 * !fp->aux->verifier_zext. Emit NOP otherwise.
+				 *
+				 * Note that "li reg_h,0" is emitted for BPF_B/H/W case,
+				 * if necessary. So, jump there insted of emitting an
+				 * additional "li reg_h,0" instruction.
+				 */
+				if (size == BPF_DW && !fp->aux->verifier_zext)
+					EMIT(PPC_RAW_LI(dst_reg_h, 0));
+				else
+					EMIT(PPC_RAW_NOP());
+				/*
+				 * Need to jump two instructions instead of one for BPF_DW case
+				 * as there are two load instructions for dst_reg_h & dst_reg
+				 * respectively.
+				 */
+				if (size == BPF_DW)
+					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));
-- 
2.31.1


  parent reply	other threads:[~2021-09-29 11:20 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
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 ` Hari Bathini [this message]
2021-09-29 11:45   ` [PATCH v4 8/8] bpf ppc32: Access only if addr is kernel address 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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