CVE-2024-42063: bpf: Mark bpf prog stack with kmsan_unposion_memory in interpreter mode

In the Linux kernel, the following vulnerability has been resolved:

bpf: Mark bpf prog stack with kmsanunposionmemory in interpreter mode

syzbot reported uninit memory usages during map{lookup,delete}elem.

========== BUG: KMSAN: uninit-value in devmaplookupelem kernel/bpf/devmap.c:441 [inline] BUG: KMSAN: uninit-value in devmaplookupelem+0xf3/0x170 kernel/bpf/devmap.c:796 devmaplookupelem kernel/bpf/devmap.c:441 [inline] devmaplookupelem+0xf3/0x170 kernel/bpf/devmap.c:796 bpfmaplookupelem kernel/bpf/helpers.c:42 [inline] bpfmaplookupelem+0x5c/0x80 kernel/bpf/helpers.c:38 bpfprogrun+0x13fe/0xe0f0 kernel/bpf/core.c:1997 bpfprogrun256+0xb5/0xe0 kernel/bpf/core.c:2237 ==========

The reproducer should be in the interpreter mode.

The C reproducer is trying to run the following bpf prog:

0: (18) r0 = 0x0 2: (18) r1 = map[id:49] 4: (b7) r8 = 16777216 5: (7b) (u64 )(r10 -8) = r8 6: (bf) r2 = r10 7: (07) r2 += -229 ^^^^^^^^^^

8: (b7) r3 = 8 9: (b7) r4 = 0 10: (85) call devmaplookupelem#1543472 11: (95) exit

It is due to the "void key" (r2) passed to the helper. bpf allows uninit stack memory access for bpf prog with the right privileges. This patch uses kmsanunpoisonmemory() to mark the stack as initialized.

This should address different syzbot reports on the uninit "void key" argument during map{lookup,delete}elem.