linux-kernel - [PATCH 06/11] x86/mm/64: In vmalloc_fault(), use CR3 instead of current->active

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Message-Id: <4650d7674185f165ed8fdf9ac4c5c35c5c179ba8.1468527351.git.luto@kernel.org>
Date:	Thu, 14 Jul 2016 13:22:54 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, Brian Gerst <brgerst@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 06/11] x86/mm/64: In vmalloc_fault(), use CR3 instead of current->active_mm

If we get a vmalloc fault while current->active_mm->pgd doesn't
match CR3, we'll crash without this change.  I've seen this failure
mode on heavily instrumented kernels with virtually mapped stacks.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/mm/fault.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 7d1fa7cd2374..ca44e2e7fd00 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -439,7 +439,7 @@ static noinline int vmalloc_fault(unsigned long address)
 	 * happen within a race in page table update. In the later
 	 * case just flush:
 	 */
-	pgd = pgd_offset(current->active_mm, address);
+	pgd = (pgd_t *)__va(read_cr3()) + pgd_index(address);
 	pgd_ref = pgd_offset_k(address);
 	if (pgd_none(*pgd_ref))
 		return -1;
-- 
2.7.4