On Sat, Mar 02, 2024 at 02:43:12PM +0800, Kefeng Wang wrote: > The rounddown_pow_of_two(0) is undefined, so val = 0 is not allowed in > the fault_around_bytes_set(), and leads to shift-out-of-bounds, > > UBSAN: shift-out-of-bounds in include/linux/log2.h:67:13 > shift exponent 4294967295 is too large for 64-bit type 'long unsigned int' > CPU: 7 PID: 107 Comm: sh Not tainted 6.8.0-rc6-next-20240301 #294 > Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015 > Call trace: > dump_backtrace+0x94/0xec > show_stack+0x18/0x24 > dump_stack_lvl+0x78/0x90 > dump_stack+0x18/0x24 > ubsan_epilogue+0x10/0x44 > __ubsan_handle_shift_out_of_bounds+0x98/0x134 > fault_around_bytes_set+0xa4/0xb0 > simple_attr_write_xsigned.isra.0+0xe4/0x1ac > simple_attr_write+0x18/0x24 > debugfs_attr_write+0x4c/0x98 > vfs_write+0xd0/0x4b0 > ksys_write+0x6c/0xfc > __arm64_sys_write+0x1c/0x28 > invoke_syscall+0x44/0x104 > el0_svc_common.constprop.0+0x40/0xe0 > do_el0_svc+0x1c/0x28 > el0_svc+0x34/0xdc > el0t_64_sync_handler+0xc0/0xc4 > el0t_64_sync+0x190/0x194 > ---[ end trace ]--- > > Fix it by setting the minimum val to PAGE_SIZE. > > Reported-by: Yue Sun <samsun1006219@xxxxxxxxx> > Closes: https://lore.kernel.org/all/CAEkJfYPim6DQqW1GqCiHLdh2-eweqk1fGyXqs3JM+8e1qGge8w@xxxxxxxxxxxxxx/ > Fixes: 53d36a56d8c4 ("mm: prefer fault_around_pages to fault_around_bytes") > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> > --- > mm/memory.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index abd4f33d62c9..e17669d4f72f 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4776,7 +4776,8 @@ static int fault_around_bytes_set(void *data, u64 val) > * The minimum value is 1 page, however this results in no fault-around > * at all. See should_fault_around(). > */ > - fault_around_pages = max(rounddown_pow_of_two(val) >> PAGE_SHIFT, 1UL); > + val = max(val, PAGE_SIZE); > + fault_around_pages = rounddown_pow_of_two(val) >> PAGE_SHIFT; > > return 0; > } > -- > 2.27.0 > Thanks, this was an oversight on my part, this fix looks good: Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
