tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
1
fork

Configure Feed

Select the types of activity you want to include in your feed.

Merge branch 'bpf-fix-verifier-crash-on-bpf_neg-with-pointer-register'

Brahmajit Das says:

====================
bpf: Fix verifier crash on BPF_NEG with pointer register

This patch fixes a crash in the BPF verifier triggered when the BPF_NEG
operation is applied to a pointer-typed register. The verifier now
checks that the destination register is not a pointer before performing
the operation.

Tested with syzkaller reproducer and new BPF sefltest.
Closes: https://syzkaller.appspot.com/bug?extid=d36d5ae81e1b0a53ef58

Changes v4:
Cleaning up, instead of using __is_pointer_value it's further
simplified by checking if regs[insn->dst_reg].type of SCALAR_VALUE
Link:

Changes in v3:
using __is_pointer_value to check if register if of pointer type
Link: https://lore.kernel.org/all/20251001095613.267475-1-listout@listout.xyz/

Changes in v2:
Checking if reg->map_ptr is NULL in bpf/log.c but with cleaner approach
(wrong approach)
Link: https://lore.kernel.org/all/20250923174738.1713751-1-listout@listout.xyz/

Changes in v1:
Checking if reg->map_ptr is NULL in bpf/log.c (wrong approach)
Link: https://lore.kernel.org/all/20250923164144.1573636-1-listout@listout.xyz/
====================

Link: https://patch.msgid.link/20251001191739.2323644-1-listout@listout.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Alexei Starovoitov a1aca22d 0c342bfc

+20 -1
+2 -1
kernel/bpf/verifier.c
··· 15645 15645 } 15646 15646 15647 15647 /* check dest operand */ 15648 - if (opcode == BPF_NEG) { 15648 + if (opcode == BPF_NEG && 15649 + regs[insn->dst_reg].type == SCALAR_VALUE) { 15649 15650 err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK); 15650 15651 err = err ?: adjust_scalar_min_max_vals(env, insn, 15651 15652 &regs[insn->dst_reg],
+18
tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c
··· 146 146 : __clobber_all); 147 147 } 148 148 149 + SEC("socket") 150 + __description("map_ptr illegal alu op, map_ptr = -map_ptr") 151 + __failure __msg("R0 invalid mem access 'scalar'") 152 + __failure_unpriv __msg_unpriv("R0 pointer arithmetic prohibited") 153 + __flag(BPF_F_ANY_ALIGNMENT) 154 + __naked void map_ptr_illegal_alu_op(void) 155 + { 156 + asm volatile (" \ 157 + r0 = %[map_hash_48b] ll; \ 158 + r0 = -r0; \ 159 + r1 = 22; \ 160 + *(u64*)(r0 + 0) = r1; \ 161 + exit; \ 162 + " : 163 + : __imm_addr(map_hash_48b) 164 + : __clobber_all); 165 + } 166 + 149 167 SEC("flow_dissector") 150 168 __description("flow_keys illegal alu op with variable offset") 151 169 __failure __msg("R7 pointer arithmetic on flow_keys prohibited")