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a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=dt9VzEwgFbYA:10 a=GoEa3M9JfhUA:10 a=VwQbUJbxAAAA:8 a=pGLkceISAAAA:8 a=SqInQvk15OgGHviEjnUA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 cc=ntf awl=host:14694 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTIwMDA3NiBTYWx0ZWRfXwmfzoxR+n2PO tjCWOFSQL6sffcWFHkAMDG9//Jh8JI/x6zsmkUWA9ih4eZYoFGjzX7F53lP8sm0m/LpBRUWrvmf wWS8Zp0HBhwb3i3Z3tFe2/XZXdv0viTO0fEfBBZgQ2zlqDq3st0WSL6lRzJWQQyCCmv0bZWo8el WrbxDQ5Z+8fJijXldZnpskdcAAETBrZmavoYaIM8G2GbzM30/OxqTT77xKTagwQMsjTTyjyOLRF EyGp6+lzfhQA4AVqDoBmNbwrkvTejfr12kY20krwwI6+qS5SmwJA9Dj1GyEFfgBxjki9pLYFJmU B+abjSU/AHv1+oRdf4YDIjf+2YMZ0Cunx5n5ugnQT9/EbeeVun+8b2r2hPsVY4nRweIFEGxhPJg XSh3ryOwZFfFYaGwqrDl08UwxYfNuEvc/AnQoJW7mvirs52C4aWIrnPVdcr9WML0ilZbRsQ1 X-Proofpoint-GUID: QYF-GHq1I7A6lCgFcDGHpx-wxHGfwnbD X-Proofpoint-ORIG-GUID: QYF-GHq1I7A6lCgFcDGHpx-wxHGfwnbD On Tue, May 20, 2025 at 11:09:05AM +0200, David Hildenbrand wrote: > On 20.05.25 07:23, Lorenzo Stoakes wrote: > > On Tue, May 20, 2025 at 01:01:38AM +0200, Jann Horn wrote: > > > On Tue, May 20, 2025 at 12:33 AM Usama Arif wrote: > > > > This is set via the new PR_SET_THP_POLICY prctl. It has 2 affects: > > > > - It sets VM_HUGEPAGE and clears VM_NOHUGEPAGE on the default VMA flags > > > > (def_flags). This means that every new VMA will be considered for > > > > hugepage. > > > > - Iterate through every VMA in the process and call hugepage_madvise > > > > on it, with MADV_HUGEPAGE policy. > > > > The policy is inherited during fork+exec. > > > > > > As I replied to Lorenzo's series > > > (https://lore.kernel.org/all/CAG48ez3-7EnBVEjpdoW7z5K0hX41nLQN5Wb65Vg-1p8DdXRnjg@mail.gmail.com/), > > > it would be nice if you could avoid introducing new flags that have > > > the combination of all the following properties: > > > > > > 1. persists across exec > > > 2. not cleared on secureexec execution > > > 3. settable without ns_capable(CAP_SYS_ADMIN) > > > 4. settable without NO_NEW_PRIVS > > > > > > Flags that have all of these properties need to be reviewed extra > > > carefully to see if there is any way they could impact the security of > > > setuid binaries, for example by changing mmap() behavior in a way that > > > makes addresses significantly more predictable. > > > > Indeed, this series was meant to be as RFC as mine while we still figured this > > out :) grr. Well, with the NACK it is - in effect - now an RFC. > > > > Yes having something persistent like this is not great, the idea of > > introducing this in my series was to provide an alternative generic version > > of this approach that can be better controlled and isn't just a 'tacked on' > > change specific to one company's needs but rather a more general idea of > > 'madvise() by default'. > > > > I do wonder in this case, whether we need be so cautious however given the > > _relatively_ safe nature of these flags? > > Yes. Changing VM_HUGEPAGE / VM_NOHUGEPAGE defaults should have little > impact, but we better be careful. > > setuid execution is certainly an interesting point. Maybe the general rule > should be, that it is not inherited over secureexec unless CAP_SYS_ADMIN? I think probably we should just restrict this operation to system admins anyway. This will be the most cautious option, and simplifies things as we then don't have to especially check for things at certain points? > > -- > Cheers, > > David / dhildenb >