On Mon, Jun 26, 2023 at 09:54:50AM +0100, Lee Jones wrote: > Dear Stable, > > On Fri, 16 Jun 2023, tip-bot2 for Lee Jones wrote: > > > The following commit has been merged into the x86/urgent branch of tip: > > > > Commit-ID: d082d48737c75d2b3cc1f972b8c8674c25131534 > > Gitweb: https://git.kernel.org/tip/d082d48737c75d2b3cc1f972b8c8674c25131534 > > Author: Lee Jones <lee@xxxxxxxxxx> > > AuthorDate: Wed, 14 Jun 2023 17:38:54 +01:00 > > Committer: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > > CommitterDate: Fri, 16 Jun 2023 11:46:42 -07:00 > > > > x86/mm: Avoid using set_pgd() outside of real PGD pages > > > > KPTI keeps around two PGDs: one for userspace and another for the > > kernel. Among other things, set_pgd() contains infrastructure to > > ensure that updates to the kernel PGD are reflected in the user PGD > > as well. > > > > One side-effect of this is that set_pgd() expects to be passed whole > > pages. Unfortunately, init_trampoline_kaslr() passes in a single entry: > > 'trampoline_pgd_entry'. > > > > When KPTI is on, set_pgd() will update 'trampoline_pgd_entry' (an > > 8-Byte globally stored [.bss] variable) and will then proceed to > > replicate that value into the non-existent neighboring user page > > (located +4k away), leading to the corruption of other global [.bss] > > stored variables. > > > > Fix it by directly assigning 'trampoline_pgd_entry' and avoiding > > set_pgd(). > > > > [ dhansen: tweak subject and changelog ] > > > > Fixes: 0925dda5962e ("x86/mm/KASLR: Use only one PUD entry for real mode trampoline") > > Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > > Signed-off-by: Lee Jones <lee@xxxxxxxxxx> > > Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > > Cc: <stable@xxxxxxxxxxxxxxx> > > Link: https://lore.kernel.org/all/20230614163859.924309-1-lee@xxxxxxxxxx/g > > --- > > arch/x86/mm/kaslr.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c > > index 557f0fe..37db264 100644 > > --- a/arch/x86/mm/kaslr.c > > +++ b/arch/x86/mm/kaslr.c > > @@ -172,10 +172,10 @@ void __meminit init_trampoline_kaslr(void) > > set_p4d(p4d_tramp, > > __p4d(_KERNPG_TABLE | __pa(pud_page_tramp))); > > > > - set_pgd(&trampoline_pgd_entry, > > - __pgd(_KERNPG_TABLE | __pa(p4d_page_tramp))); > > + trampoline_pgd_entry = > > + __pgd(_KERNPG_TABLE | __pa(p4d_page_tramp)); > > } else { > > - set_pgd(&trampoline_pgd_entry, > > - __pgd(_KERNPG_TABLE | __pa(pud_page_tramp))); > > + trampoline_pgd_entry = > > + __pgd(_KERNPG_TABLE | __pa(pud_page_tramp)); > > } > > } > > Could we have this expedited please? There are users waiting for it. > > Upstream commit is: > > d082d48737c75 ("x86/mm: Avoid using set_pgd() outside of real PGD pages") Please look through your emails you got this weekend, it's already queued up in the following stable trees: queue-5.4 queue-5.10 queue-5.15 queue-6.1 queue-6.3 greg k-h
