Commit e919c0b2 authored by Hari Bathini's avatar Hari Bathini Committed by Michael Ellerman
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bpf ppc32: Access only if addr is kernel address 



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: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarHari Bathini <hbathini@linux.ibm.com>
Reviewed-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211012123056.485795-9-hbathini@linux.ibm.com
parent 23b51916

arch/powerpc/net/bpf_jit_comp32.c

+34 −0
Original line number Diff line number Diff line
@@ -820,6 +820,40 @@ 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));