From: Lee Jones lee@kernel.org
commit d082d48737c75d2b3cc1f972b8c8674c25131534 upstream.
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@linux.intel.com Signed-off-by: Lee Jones lee@kernel.org Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20230614163859.924309-1-lee@kernel.org/g Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/mm/kaslr.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
--- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -182,11 +182,11 @@ static void __meminit init_trampoline_pu 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)); } }