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dmarc=pass (policy=none) header.from=oracle.com ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1666124755; a=rsa-sha256; cv=pass; b=clHWn0X0oP9PRBTdJteybvDb2fNrq4No80hu2Fa8M4BgfouL2HsXmx7PgZlZjjt1bT5Aug 9JcGBI2KA8GPBTgDKtOjbFZeQMFwuS8QE3bu2JSxPUIyRCMDyUnLr+aTEiCRTnPsmCjJrd qGatPQ1onpmMxjmlwSul2/Cgr+DAaXw= Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2022-7-12 header.b=TCjTWKSt; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=HwaQ3iVH; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf30.hostedemail.com: domain of liam.howlett@oracle.com designates 205.220.177.32 as permitted sender) smtp.mailfrom=liam.howlett@oracle.com; dmarc=pass (policy=none) header.from=oracle.com X-Stat-Signature: ibftdy3pojicj6nofa3yxq9ozechxb8a X-Rspamd-Queue-Id: 9910F80024 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1666124755-750024 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: * David Hildenbrand [221018 15:27]: > On 18.10.22 21:17, Liam Howlett wrote: > > mmap should return the start address of newly mapped area when > > successful. On a successful merge of a VMA, the return address was > > changed and thus was violating that expectation from userspace. > >=20 >=20 > Just wondering, do we have a simple user space reproducer / test? Not today, no. >=20 > Do we want to add some more tests for such scenarios? Yes, I will code something up for LTP. >=20 > > This is a restoration of functionality provided by 309d08d9b3a3 > > (mm/mmap.c: fix mmap return value when vma is merged after call_mmap())= . > > For completeness of fixing MAP_FIXED, implement the comments from the > > previous discussion to never update the address and fail if the address > > changes. Leaving the error as a WARN_ON() to avoid crashing the kernel= . > >=20 > > Cc: Liu Zixian > > Cc: David Hildenbrand > > Cc: Jason Gunthorpe > > Cc: Matthew Wilcox > > Link: https://lore.kernel.org/all/Y06yk66SKxlrwwfb@lakrids/ > > Link: https://lore.kernel.org/all/20201203085350.22624-1-liuzixian4@hua= wei.com/ > > Fixes: 4dd1b84140c1 (mm/mmap: use advanced maple tree API for mmap_regi= on()) > > Reported-by: Mark Rutland > > Signed-off-by: Liam R. Howlett > > --- > > mm/mmap.c | 15 +++++++-------- > > 1 file changed, 7 insertions(+), 8 deletions(-) > >=20 > > diff --git a/mm/mmap.c b/mm/mmap.c > > index 42cd2c260898..22010e13f1a1 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -2625,14 +2625,14 @@ unsigned long mmap_region(struct file *file, un= signed long addr, > > if (error) > > goto unmap_and_free_vma; > > - /* Can addr have changed?? > > - * > > - * Answer: Yes, several device drivers can do it in their > > - * f_op->mmap method. -DaveM > > + /* > > + * Expansion is handled above, merging is handled below. > > + * Drivers should not alter the address of the VMA. > > */ > > - WARN_ON_ONCE(addr !=3D vma->vm_start); > > - > > - addr =3D vma->vm_start; > > + if (WARN_ON((addr !=3D vma->vm_start))) { > > + error =3D -EINVAL; > > + goto close_and_free_vma; > > + } >=20 > If this is something that user space can trigger, WARN_* is the wrong > choice. But what I understand from the comment change is that this must n= ot > happen at that point unless there is a real issue. The VMA start address could be changed in call_mmap() which is a driver call. I guess someone could write a driver to mmap by a users action? I don't think it can be reached other ways. In any case, I'm changing a WARN_ON_ONCE() to a WARN_ON() and undoing the badness instead of marching forwards. >=20 > Why not "if (WARN_ON_ONCE)" ? I was thinking it was harder to ignore if it happen more frequently? There isn't a driver that does this now, but I'm not picky over which variant to call. Thanks, Liam=