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Karpov" Cc: harry@kernel.org, akpm@linux-foundation.org, Liam.Howlett@oracle.com, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, peterx@redhat.com, pfalcato@suse.de, brauner@kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, usama.arif@linux.dev Subject: Re: [PATCH v2] userfaultfd: allow registration of ranges below mmap_min_addr Message-ID: References: <20260409103345.15044-1-komlomal@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260409103345.15044-1-komlomal@gmail.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: BC6EF14000E X-Stat-Signature: pzxusips5fsfbap4dxgihfqiee6oxbjg X-Rspam-User: X-HE-Tag: 1775747606-789791 X-HE-Meta: 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 TOWkABHq FPZkJ1yjJCkZ/SqOYg0e1jKAkruDUKLAcJAINy+ywX6FyRzzVRxGMZk6RJDCiDT6ILxR2Xyh2xRXlySoQHAhTN5zvkrhAlNYiZImyjgagCgnPMFfBSLsTLCPnqMqLPV8Gv8Y5N4tFDBccLEEvp8QY3EwHPz5lDBGjo4kmz1bf7F1blXxvaIGf+oAlT+vUw8aHZooulKL6fdY03m438nqukhEjgZ1O2wBhXOVv78lhqvl0eH7VvAzMWBoCkTb/rUtPnI9uxLNlW3fzLWXHV+8/ObyANgIGe5KB+m30scw7aRqsP3Bh6SypZ1XnpRFPi1eDOmyoaAxYSZC654783W4GBiCZ1s5rZqvnkb4b Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 09, 2026 at 01:33:45PM +0300, Denis M. Karpov wrote: > The current implementation of validate_range() in fs/userfaultfd.c > performs a hard check against mmap_min_addr. This is redundant because > UFFDIO_REGISTER operates on memory ranges that must already be backed > by a VMA. > > Enforcing mmap_min_addr or capability checks again in userfaultfd is > unnecessary and prevents applications like binary compilers from > using UFFD for valid memory regions mapped by application. > > Remove the redundant check for mmap_min_addr. > > Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") > Signed-off-by: Denis M. Karpov Reviewed-by: Mike Rapoport (Microsoft) > --- > v2: > - Remove the check entirely rather than replacing it, as suggested by > Harry Yoo and Lorenzo Stoakes. > - Added Fixes tag. > - Link to v1: https://lore.kernel.org/r/20260407081442.6256-1-komlomal@gmail.com > --- > fs/userfaultfd.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index bdc84e521..4b53dc4a3 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1238,8 +1238,6 @@ static __always_inline int validate_unaligned_range( > return -EINVAL; > if (!len) > return -EINVAL; > - if (start < mmap_min_addr) > - return -EINVAL; > if (start >= task_size) > return -EINVAL; > if (len > task_size - start) > -- > 2.43.0 > -- Sincerely yours, Mike.