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)); } }
