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bpf ppc32: Access only if addr is kernel address

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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>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211012123056.485795-9-hbathini@linux.ibm.com
This commit is contained in:
Hari Bathini 2021-10-12 18:00:56 +05:30 committed by Michael Ellerman
parent 23b51916ee
commit e919c0b232
1 changed files with 34 additions and 0 deletions
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34
arch/powerpc/net/bpf_jit_comp32.c
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@ -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));