powerpc/code-patching: Fix KASAN hit by not flagging text patching area as VM_ALLOC

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

powerpc/code-patching: Fix KASAN hit by not flagging text patching area as VM_ALLOC

Erhard reported the following KASAN hit while booting his PowerMac G4

with a KASAN-enabled kernel 6.13-rc6:

BUG: KASAN: vmalloc-out-of-bounds in copy_to_kernel_nofault+0xd8/0x1c8

Write of size 8 at addr f1000000 by task chronyd/1293

CPU: 0 UID: 123 PID: 1293 Comm: chronyd Tainted: G W 6.13.0-rc6-PMacG4 #2

Tainted: [W]=WARN

Hardware name: PowerMac3,6 7455 0x80010303 PowerMac

Call Trace:

[c2437590] [c1631a84] dump_stack_lvl+0x70/0x8c (unreliable)

[c24375b0] [c0504998] print_report+0xdc/0x504

[c2437610] [c050475c] kasan_report+0xf8/0x108

[c2437690] [c0505a3c] kasan_check_range+0x24/0x18c

[c24376a0] [c03fb5e4] copy_to_kernel_nofault+0xd8/0x1c8

[c24376c0] [c004c014] patch_instructions+0x15c/0x16c

[c2437710] [c00731a8] bpf_arch_text_copy+0x60/0x7c

[c2437730] [c0281168] bpf_jit_binary_pack_finalize+0x50/0xac

[c2437750] [c0073cf4] bpf_int_jit_compile+0xb30/0xdec

[c2437880] [c0280394] bpf_prog_select_runtime+0x15c/0x478

[c24378d0] [c1263428] bpf_prepare_filter+0xbf8/0xc14

[c2437990] [c12677ec] bpf_prog_create_from_user+0x258/0x2b4

[c24379d0] [c027111c] do_seccomp+0x3dc/0x1890

[c2437ac0] [c001d8e0] system_call_exception+0x2dc/0x420

[c2437f30] [c00281ac] ret_from_syscall+0x0/0x2c

--- interrupt: c00 at 0x5a1274

NIP: 005a1274 LR: 006a3b3c CTR: 005296c8

REGS: c2437f40 TRAP: 0c00 Tainted: G W (6.13.0-rc6-PMacG4)

MSR: 0200f932 <VEC,EE,PR,FP,ME,IR,DR,RI> CR: 24004422 XER: 00000000

GPR00: 00000166 af8f3fa0 a7ee3540 00000001 00000000 013b6500 005a5858 0200f932

GPR08: 00000000 00001fe9 013d5fc8 005296c8 2822244c 00b2fcd8 00000000 af8f4b57

GPR16: 00000000 00000001 00000000 00000000 00000000 00000001 00000000 00000002

GPR24: 00afdbb0 00000000 00000000 00000000 006e0004 013ce060 006e7c1c 00000001

NIP [005a1274] 0x5a1274

LR [006a3b3c] 0x6a3b3c

--- interrupt: c00

The buggy address belongs to the virtual mapping at

[f1000000, f1002000) created by:

text_area_cpu_up+0x20/0x190

The buggy address belongs to the physical page:

page: refcount:1 mapcount:0 mapping:00000000 index:0x0 pfn:0x76e30

flags: 0x80000000(zone=2)

raw: 80000000 00000000 00000122 00000000 00000000 00000000 ffffffff 00000001

raw: 00000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

f0ffff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

f0ffff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

>f1000000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8

^

f1000080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8

f1000100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8

==================================================================

f8 corresponds to KASAN_VMALLOC_INVALID which means the area is not

initialised hence not supposed to be used yet.

Powerpc text patching infrastructure allocates a virtual memory area

using get_vm_area() and flags it as VM_ALLOC. But that flag is meant

to be used for vmalloc() and vmalloc() allocated memory is not

supposed to be used before a call to __vmalloc_node_range() which is

never called for that area.

That went undetected until commit e4137f08816b ("mm, kasan, kmsan:

instrument copy_from/to_kernel_nofault")

The area allocated by text_area_cpu_up() is not vmalloc memory, it is

mapped directly on demand when needed by map_kernel_page(). There is

no VM flag corresponding to such usage, so just pass no flag. That way

the area will be unpoisonned and usable immediately.