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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 7A874100010 X-Rspamd-Server: rspam05 X-Stat-Signature: qesu5tmp4ztoj6hxqc6n7uo4ak7nibdn X-Rspam-User: X-HE-Tag: 1759214755-869502 X-HE-Meta: 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 xUvVGHKm 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 30.09.25 08:39, Jakub Acs wrote: > syzkaller discovered the following crash: (kernel BUG) > > [ 44.607039] ------------[ cut here ]------------ > [ 44.607422] kernel BUG at mm/userfaultfd.c:2067! > [ 44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI > [ 44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none) > [ 44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 > [ 44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460 > > > > [ 44.617726] Call Trace: > [ 44.617926] > [ 44.619284] userfaultfd_release+0xef/0x1b0 > [ 44.620976] __fput+0x3f9/0xb60 > [ 44.621240] fput_close_sync+0x110/0x210 > [ 44.622222] __x64_sys_close+0x8f/0x120 > [ 44.622530] do_syscall_64+0x5b/0x2f0 > [ 44.622840] entry_SYSCALL_64_after_hwframe+0x76/0x7e > [ 44.623244] RIP: 0033:0x7f365bb3f227 > > Kernel panics because it detects UFFD inconsistency during > userfaultfd_release_all(). Specifically, a VMA which has a valid pointer > to vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags. > > The inconsistency is caused in ksm_madvise(): when user calls madvise() > with MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR > mode, it accidentally clears all flags stored in the upper 32 bits of > vma->vm_flags. > > Assuming x86_64 kernel build, unsigned long is 64-bit and unsigned int > and int are 32-bit wide. This setup causes the following mishap during > the &= ~VM_MERGEABLE assignment. > > VM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000'0000. > After ~ is applied, it becomes 0x7fff'ffff unsigned int, which is then > promoted to unsigned long before the & operation. This promotion fills > upper 32 bits with leading 0s, as we're doing unsigned conversion (and > even for a signed conversion, this wouldn't help as the leading bit is > 0). & operation thus ends up AND-ing vm_flags with 0x0000'0000'7fff'ffff > instead of intended 0xffff'ffff'7fff'ffff and hence accidentally clears > the upper 32-bits of its value. > > Fix it by casting `VM_MERGEABLE` constant to unsigned long to preserve > the upper 32 bits, in case it's needed. > > Note: other VM_* flags are not affected: > This only happens to the VM_MERGEABLE flag, as the other VM_* flags are > all constants of type int and after ~ operation, they end up with > leading 1 and are thus converted to unsigned long with leading 1s. > > Note 2: > After commit 31defc3b01d9 ("userfaultfd: remove (VM_)BUG_ON()s"), this is > no longer a kernel BUG, but a WARNING at the same place: > > [ 45.595973] WARNING: CPU: 1 PID: 2474 at mm/userfaultfd.c:2067 > > but the root-cause (flag-drop) remains the same. > > Fixes: 7677f7fd8be76 ("userfaultfd: add minor fault registration mode") > Signed-off-by: Jakub Acs > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Xu Xin > Cc: Chengming Zhou > Cc: Peter Xu > Cc: Axel Rasmussen > Cc: Mike Kravetz > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Cc: stable@vger.kernel.org > --- > > I looked around the kernel and found one more flag that might be > causing similar issues: "IORESOURCE_BUSY" - as its inverted version is > bit-anded to unsigned long fields. However, it seems those fields don't > actually use any bits from upper 32-bits as flags (yet?). > > I also considered changing the constant definition by adding ULL, but am > not sure where else that could blow up, plus it would likely call to > define all the related constants as ULL for consistency. If you'd prefer > that fix, let me know. > > > mm/ksm.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index 160787bb121c..c24137a1eeb7 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -2871,7 +2871,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start, > return err; > } > > - *vm_flags &= ~VM_MERGEABLE; > + *vm_flags &= ~((unsigned long) VM_MERGEABLE); > break; > } > Wouldn't it be better to just do diff --git a/include/linux/mm.h b/include/linux/mm.h index 1ae97a0b8ec75..0eaf8af153f98 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -296,7 +296,7 @@ extern unsigned int kobjsize(const void *objp); #define VM_MIXEDMAP 0x10000000 /* Can contain "struct page" and pure PFN pages */ #define VM_HUGEPAGE 0x20000000 /* MADV_HUGEPAGE marked this vma */ #define VM_NOHUGEPAGE 0x40000000 /* MADV_NOHUGEPAGE marked this vma */ -#define VM_MERGEABLE 0x80000000 /* KSM may merge identical pages */ +#define VM_MERGEABLE 0x80000000ul /* KSM may merge identical pages */ #ifdef CONFIG_ARCH_USES_HIGH_VMA_FLAGS #define VM_HIGH_ARCH_BIT_0 32 /* bit only usable on 64-bit architectures */ And for consistency doing it to all other flags as well? After all we have typedef unsigned long vm_flags_t; -- Cheers David / dhildenb