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>

Author: Alexei Starovoitov

kernel/bpf/verifier.c

@@ -15645,7 +15645,8 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
 		}
 
 		/* check dest operand */
-		if (opcode == BPF_NEG) {
+		if (opcode == BPF_NEG &&
+		    regs[insn->dst_reg].type == SCALAR_VALUE) {
 			err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
 			err = err ?: adjust_scalar_min_max_vals(env, insn,
 							 &regs[insn->dst_reg],

tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c

@@ -146,6 +146,24 @@ l0_%=:	exit;						\
 	: __clobber_all);
 }
 
+SEC("socket")
+__description("map_ptr illegal alu op, map_ptr = -map_ptr")
+__failure __msg("R0 invalid mem access 'scalar'")
+__failure_unpriv __msg_unpriv("R0 pointer arithmetic prohibited")
+__flag(BPF_F_ANY_ALIGNMENT)
+__naked void map_ptr_illegal_alu_op(void)
+{
+	asm volatile ("					\
+	r0 = %[map_hash_48b] ll;			\
+	r0 = -r0;					\
+	r1 = 22;					\
+	*(u64*)(r0 + 0) = r1;				\
+	exit;						\
+"	:
+	: __imm_addr(map_hash_48b)
+	: __clobber_all);
+}
+
 SEC("flow_dissector")
 __description("flow_keys illegal alu op with variable offset")
 __failure __msg("R7 pointer arithmetic on flow_keys prohibited")