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Message-ID: <168694160067.404.13343792487331756749.tip-bot2@tip-bot2>
Date: Fri, 16 Jun 2023 18:53:20 -0000
From: "tip-bot2 for Lee Jones" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
Lee Jones <lee@...nel.org>, <stable@...r.kernel.org>,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/mm: Avoid using set_pgd() outside of real PGD pages
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@...nel.org>
AuthorDate: Wed, 14 Jun 2023 17:38:54 +01:00
Committer: Dave Hansen <dave.hansen@...ux.intel.com>
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@...ux.intel.com>
Signed-off-by: Lee Jones <lee@...nel.org>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: <stable@...r.kernel.org>
Link: https://lore.kernel.org/all/20230614163859.924309-1-lee@kernel.org/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));
}
}
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