Christophe Leroy <christophe.le...@csgroup.eu> writes:
> Erhard reports the following KASAN hit on Talos II (power9) with kernel 6.13:
>
> [ 12.028126]
> ==================================================================
> [ 12.028198] BUG: KASAN: user-memory-access in
> copy_to_kernel_nofault+0x8c/0x1a0
> [ 12.028260] Write of size 8 at addr 0000187e458f2000 by task systemd/1
>
> [ 12.028346] CPU: 87 UID: 0 PID: 1 Comm: systemd Tainted: G
> T 6.13.0-P9-dirty #3
> [ 12.028408] Tainted: [T]=RANDSTRUCT
> [ 12.028446] Hardware name: T2P9D01 REV 1.01 POWER9 0x4e1202
> opal:skiboot-bc106a0 PowerNV
> [ 12.028500] Call Trace:
> [ 12.028536] [c000000008dbf3b0] [c000000001656a48]
> dump_stack_lvl+0xbc/0x110 (unreliable)
> [ 12.028609] [c000000008dbf3f0] [c0000000006e2fc8] print_report+0x6b0/0x708
> [ 12.028666] [c000000008dbf4e0] [c0000000006e2454] kasan_report+0x164/0x300
> [ 12.028725] [c000000008dbf600] [c0000000006e54d4]
> kasan_check_range+0x314/0x370
> [ 12.028784] [c000000008dbf640] [c0000000006e6310]
> __kasan_check_write+0x20/0x40
> [ 12.028842] [c000000008dbf660] [c000000000578e8c]
> copy_to_kernel_nofault+0x8c/0x1a0
> [ 12.028902] [c000000008dbf6a0] [c0000000000acfe4]
> __patch_instructions+0x194/0x210
> [ 12.028965] [c000000008dbf6e0] [c0000000000ade80]
> patch_instructions+0x150/0x590
> [ 12.029026] [c000000008dbf7c0] [c0000000001159bc]
> bpf_arch_text_copy+0x6c/0xe0
> [ 12.029085] [c000000008dbf800] [c000000000424250]
> bpf_jit_binary_pack_finalize+0x40/0xc0
> [ 12.029147] [c000000008dbf830] [c000000000115dec]
> bpf_int_jit_compile+0x3bc/0x930
> [ 12.029206] [c000000008dbf990] [c000000000423720]
> bpf_prog_select_runtime+0x1f0/0x280
> [ 12.029266] [c000000008dbfa00] [c000000000434b18]
> bpf_prog_load+0xbb8/0x1370
> [ 12.029324] [c000000008dbfb70] [c000000000436ebc] __sys_bpf+0x5ac/0x2e00
> [ 12.029379] [c000000008dbfd00] [c00000000043a228] sys_bpf+0x28/0x40
> [ 12.029435] [c000000008dbfd20] [c000000000038eb4]
> system_call_exception+0x334/0x610
> [ 12.029497] [c000000008dbfe50] [c00000000000c270]
> system_call_vectored_common+0xf0/0x280
> [ 12.029561] --- interrupt: 3000 at 0x3fff82f5cfa8
> [ 12.029608] NIP: 00003fff82f5cfa8 LR: 00003fff82f5cfa8 CTR:
> 0000000000000000
> [ 12.029660] REGS: c000000008dbfe80 TRAP: 3000 Tainted: G
> T (6.13.0-P9-dirty)
> [ 12.029735] MSR: 900000000280f032 <SF,HV,VEC,VSX,EE,PR,FP,ME,IR,DR,RI>
> CR: 42004848 XER: 00000000
> [ 12.029855] IRQMASK: 0
> GPR00: 0000000000000169 00003fffdcf789a0 00003fff83067100
> 0000000000000005
> GPR04: 00003fffdcf78a98 0000000000000090 0000000000000000
> 0000000000000008
> GPR08: 0000000000000000 0000000000000000 0000000000000000
> 0000000000000000
> GPR12: 0000000000000000 00003fff836ff7e0 c000000000010678
> 0000000000000000
> GPR16: 0000000000000000 0000000000000000 00003fffdcf78f28
> 00003fffdcf78f90
> GPR20: 0000000000000000 0000000000000000 0000000000000000
> 00003fffdcf78f80
> GPR24: 00003fffdcf78f70 00003fffdcf78d10 00003fff835c7239
> 00003fffdcf78bd8
> GPR28: 00003fffdcf78a98 0000000000000000 0000000000000000
> 000000011f547580
> [ 12.030316] NIP [00003fff82f5cfa8] 0x3fff82f5cfa8
> [ 12.030361] LR [00003fff82f5cfa8] 0x3fff82f5cfa8
> [ 12.030405] --- interrupt: 3000
> [ 12.030444]
> ==================================================================
>
> Commit c28c15b6d28a ("powerpc/code-patching: Use temporary mm for
> Radix MMU") is inspired from x86 but unlike x86 is doesn't disable
> KASAN reports during patching. This wasn't a problem at the begining
> because __patch_mem() is not instrumented.
>
> Commit 465cabc97b42 ("powerpc/code-patching: introduce
> patch_instructions()") use copy_to_kernel_nofault() to copy several
> instructions at once. But when using temporary mm the destination is
> not regular kernel memory but a kind of kernel-like memory located
> in user address space. Because it is not in kernel address space it is
> not covered by KASAN shadow memory. Since commit e4137f08816b ("mm,
> kasan, kmsan: instrument copy_from/to_kernel_nofault") KASAN reports
> bad accesses from copy_to_kernel_nofault(). Here a bad access to user
> memory is reported because KASAN detects the lack of shadow memory and
> the address is below TASK_SIZE.
>
> Do like x86 in commit b3fd8e83ada0 ("x86/alternatives: Use temporary
> mm for text poking") and disable KASAN reports during patching when
> using temporary mm.
>
> Reported-by: Erhard Furtner <erhar...@mailbox.org>
> Close: https://lore.kernel.org/all/20250201151435.48400261@yea/
> Fixes: 465cabc97b42 ("powerpc/code-patching: introduce patch_instructions()")
> Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
> ---
> arch/powerpc/lib/code-patching.c | 2 ++
> 1 file changed, 2 insertions(+)
Thanks for debugging that Christophe.
Fix looks good to me.
Acked-by: Michael Ellerman <m...@ellerman.id.au>
cheers
