Commit-ID: eac7073aa69aa1cac819aa712146284f53f642b1
Gitweb: https://git.kernel.org/tip/eac7073aa69aa1cac819aa712146284f53f642b1
Author: Dave Hansen <[email protected]>
AuthorDate: Thu, 2 Aug 2018 15:58:25 -0700
Committer: Thomas Gleixner <[email protected]>
CommitDate: Sun, 5 Aug 2018 22:21:02 +0200
x86/mm/pti: Clear Global bit more aggressively
The kernel image starts out with the Global bit set across the entire
kernel image. The bit is cleared with set_memory_nonglobal() in the
configurations with PCIDs where the performance benefits of the Global bit
are not needed.
However, this is fragile. It means that we are stuck opting *out* of the
less-secure (Global bit set) configuration, which seems backwards. Let's
start more secure (Global bit clear) and then let things opt back in if
they want performance, or are truly mapping common data between kernel and
userspace.
This fixes a bug. Before this patch, there are areas that are unmapped
from the user page tables (like like everything above 0xffffffff82600000 in
the example below). These have the hallmark of being a wrong Global area:
they are not identical in the 'current_kernel' and 'current_user' page
table dumps. They are also read-write, which means they're much more
likely to contain secrets.
Before this patch:
current_kernel:---[ High Kernel Mapping ]---
current_kernel-0xffffffff80000000-0xffffffff81000000 16M
pmd
current_kernel-0xffffffff81000000-0xffffffff81e00000 14M ro
PSE GLB x pmd
current_kernel-0xffffffff81e00000-0xffffffff81e11000 68K ro
GLB x pte
current_kernel-0xffffffff81e11000-0xffffffff82000000 1980K RW
GLB NX pte
current_kernel-0xffffffff82000000-0xffffffff82600000 6M ro
PSE GLB NX pmd
current_kernel-0xffffffff82600000-0xffffffff82c00000 6M RW
PSE GLB NX pmd
current_kernel-0xffffffff82c00000-0xffffffff82e00000 2M RW
GLB NX pte
current_kernel-0xffffffff82e00000-0xffffffff83200000 4M RW
PSE GLB NX pmd
current_kernel-0xffffffff83200000-0xffffffffa0000000 462M
pmd
current_user:---[ High Kernel Mapping ]---
current_user-0xffffffff80000000-0xffffffff81000000 16M
pmd
current_user-0xffffffff81000000-0xffffffff81e00000 14M ro
PSE GLB x pmd
current_user-0xffffffff81e00000-0xffffffff81e11000 68K ro
GLB x pte
current_user-0xffffffff81e11000-0xffffffff82000000 1980K RW
GLB NX pte
current_user-0xffffffff82000000-0xffffffff82600000 6M ro
PSE GLB NX pmd
current_user-0xffffffff82600000-0xffffffffa0000000 474M
pmd
After this patch:
current_kernel:---[ High Kernel Mapping ]---
current_kernel-0xffffffff80000000-0xffffffff81000000 16M
pmd
current_kernel-0xffffffff81000000-0xffffffff81e00000 14M ro
PSE GLB x pmd
current_kernel-0xffffffff81e00000-0xffffffff81e11000 68K ro
GLB x pte
current_kernel-0xffffffff81e11000-0xffffffff82000000 1980K RW
NX pte
current_kernel-0xffffffff82000000-0xffffffff82600000 6M ro
PSE GLB NX pmd
current_kernel-0xffffffff82600000-0xffffffff82c00000 6M RW
PSE NX pmd
current_kernel-0xffffffff82c00000-0xffffffff82e00000 2M RW
NX pte
current_kernel-0xffffffff82e00000-0xffffffff83200000 4M RW
PSE NX pmd
current_kernel-0xffffffff83200000-0xffffffffa0000000 462M
pmd
current_user:---[ High Kernel Mapping ]---
current_user-0xffffffff80000000-0xffffffff81000000 16M
pmd
current_user-0xffffffff81000000-0xffffffff81e00000 14M ro
PSE GLB x pmd
current_user-0xffffffff81e00000-0xffffffff81e11000 68K ro
GLB x pte
current_user-0xffffffff81e11000-0xffffffff82000000 1980K RW
NX pte
current_user-0xffffffff82000000-0xffffffff82600000 6M ro
PSE GLB NX pmd
current_user-0xffffffff82600000-0xffffffffa0000000 474M
pmd
Fixes: 0f561fce4d69 ("x86/pti: Enable global pages for shared areas")
Reported-by: Hugh Dickins <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Kees Cook <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Andi Kleen <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
arch/x86/mm/pageattr.c | 6 ++++++
arch/x86/mm/pti.c | 34 ++++++++++++++++++++++++----------
2 files changed, 30 insertions(+), 10 deletions(-)
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 3bded76e8d5c..c04153796f61 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1784,6 +1784,12 @@ int set_memory_nonglobal(unsigned long addr, int
numpages)
__pgprot(_PAGE_GLOBAL), 0);
}
+int set_memory_global(unsigned long addr, int numpages)
+{
+ return change_page_attr_set(&addr, numpages,
+ __pgprot(_PAGE_GLOBAL), 0);
+}
+
static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
{
struct cpa_data cpa;
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 4d418e705878..8d88d067b3d7 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -434,6 +434,13 @@ static inline bool pti_kernel_image_global_ok(void)
return true;
}
+/*
+ * This is the only user for these and it is not arch-generic
+ * like the other set_memory.h functions. Just extern them.
+ */
+extern int set_memory_nonglobal(unsigned long addr, int numpages);
+extern int set_memory_global(unsigned long addr, int numpages);
+
/*
* For some configurations, map all of kernel text into the user page
* tables. This reduces TLB misses, especially on non-PCID systems.
@@ -446,7 +453,8 @@ void pti_clone_kernel_text(void)
* clone the areas past rodata, they might contain secrets.
*/
unsigned long start = PFN_ALIGN(_text);
- unsigned long end = (unsigned long)__end_rodata_hpage_align;
+ unsigned long end_clone = (unsigned long)__end_rodata_hpage_align;
+ unsigned long end_global = PFN_ALIGN((unsigned long)__stop___ex_table);
if (!pti_kernel_image_global_ok())
return;
@@ -458,14 +466,18 @@ void pti_clone_kernel_text(void)
* pti_set_kernel_image_nonglobal() did to clear the
* global bit.
*/
- pti_clone_pmds(start, end, _PAGE_RW);
+ pti_clone_pmds(start, end_clone, _PAGE_RW);
+
+ /*
+ * pti_clone_pmds() will set the global bit in any PMDs
+ * that it clones, but we also need to get any PTEs in
+ * the last level for areas that are not huge-page-aligned.
+ */
+
+ /* Set the global bit for normal non-__init kernel text: */
+ set_memory_global(start, (end_global - start) >> PAGE_SHIFT);
}
-/*
- * This is the only user for it and it is not arch-generic like
- * the other set_memory.h functions. Just extern it.
- */
-extern int set_memory_nonglobal(unsigned long addr, int numpages);
void pti_set_kernel_image_nonglobal(void)
{
/*
@@ -477,9 +489,11 @@ void pti_set_kernel_image_nonglobal(void)
unsigned long start = PFN_ALIGN(_text);
unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE);
- if (pti_kernel_image_global_ok())
- return;
-
+ /*
+ * This clears _PAGE_GLOBAL from the entire kernel image.
+ * pti_clone_kernel_text() map put _PAGE_GLOBAL back for
+ * areas that are mapped to userspace.
+ */
set_memory_nonglobal(start, (end - start) >> PAGE_SHIFT);
}
