[PATCH] x86 : Add NX protection for kernel data on 64 bit
From: matthieu castet
Date: Sun Mar 13 2011 - 14:37:27 EST
Cpu hotplug code read data in head_64.S (phys_base) before enabling NX, so when
we enable NX on data, an triple fault happen because a reserved bit is set.
It was fixed by allocating dedicated page table for ident mapping in trampoline.
Now data can be protected by NX.
The Low kernel Mapping is also set to NX.
Finaly we preserve large page mapping by applying nx in free_init_pages only
when we switch to NX mode
mapping now look like :
---[ Low Kernel Mapping ]---
0xffff880000000000-0xffff880000200000 2M RW GLB NX pte
0xffff880000200000-0xffff880001000000 14M RW PSE GLB NX pmd
0xffff880001000000-0xffff880001200000 2M ro PSE GLB NX pmd
0xffff880001200000-0xffff8800012ae000 696K ro GLB NX pte
0xffff8800012ae000-0xffff880001400000 1352K RW GLB NX pte
0xffff880001400000-0xffff880001503000 1036K ro GLB NX pte
0xffff880001503000-0xffff880001600000 1012K RW GLB NX pte
0xffff880001600000-0xffff880007e00000 104M RW PSE GLB NX pmd
0xffff880007e00000-0xffff880007ffd000 2036K RW GLB NX pte
0xffff880007ffd000-0xffff880008000000 12K pte
0xffff880008000000-0xffff880040000000 896M pmd
0xffff880040000000-0xffff888000000000 511G pud
0xffff888000000000-0xffffc90000000000 66048G pgd
---[ vmalloc() Area ]---
[...]
---[ High Kernel Mapping ]---
0xffffffff80000000-0xffffffff81000000 16M pmd
0xffffffff81000000-0xffffffff81400000 4M ro PSE GLB x pmd
0xffffffff81400000-0xffffffff81600000 2M ro PSE GLB NX pmd
0xffffffff81600000-0xffffffff81800000 2M RW PSE GLB NX pmd
0xffffffff81800000-0xffffffffa0000000 488M pmd
---[ Modules ]---
Signed-off-by: Matthieu CASTET <castet.matthieu@xxxxxxx>
Test-by: Lin Ming <ming.m.lin@xxxxxxxxx>
---
arch/x86/kernel/head_64.S | 15 +++++++++++++++
arch/x86/kernel/trampoline_64.S | 4 ++--
arch/x86/mm/init.c | 6 ++++--
arch/x86/mm/init_64.c | 6 +++++-
4 files changed, 26 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index e11e394..e261354 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -140,6 +140,9 @@ ident_complete:
addq %rbp, trampoline_level4_pgt + 0(%rip)
addq %rbp, trampoline_level4_pgt + (511*8)(%rip)
+ addq %rbp, trampoline_level3_ident_pgt + 0(%rip)
+ addq %rbp, trampoline_level3_ident_pgt + (L3_START_KERNEL*8)(%rip)
+
/* Due to ENTRY(), sometimes the empty space gets filled with
* zeros. Better take a jmp than relying on empty space being
* filled with 0x90 (nop)
@@ -395,6 +398,18 @@ NEXT_PAGE(level2_kernel_pgt)
NEXT_PAGE(level2_spare_pgt)
.fill 512, 8, 0
+NEXT_PAGE(trampoline_level3_ident_pgt)
+ .quad trampoline_level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .fill L3_START_KERNEL-1,8,0
+ .quad trampoline_level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .fill 511-L3_START_KERNEL,8,0
+
+
+NEXT_PAGE(trampoline_level2_ident_pgt)
+ /* Since I easily can, map the first 1G.
+ * Don't set NX because code runs from these pages.
+ */
+ PMDS(0, __PAGE_KERNEL_IDENT_LARGE_EXEC, PTRS_PER_PMD)
#undef PMDS
#undef NEXT_PAGE
diff --git a/arch/x86/kernel/trampoline_64.S b/arch/x86/kernel/trampoline_64.S
index 09ff517..8723e47 100644
--- a/arch/x86/kernel/trampoline_64.S
+++ b/arch/x86/kernel/trampoline_64.S
@@ -164,8 +164,8 @@ trampoline_stack:
.org 0x1000
trampoline_stack_end:
ENTRY(trampoline_level4_pgt)
- .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .quad trampoline_level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
.fill 510,8,0
- .quad level3_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .quad trampoline_level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
ENTRY(trampoline_end)
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 286d289..98dd5fa 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -338,8 +338,10 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
* we are going to free part of that, we need to make that
* writeable and non-executable first.
*/
- set_memory_nx(begin, (end - begin) >> PAGE_SHIFT);
- set_memory_rw(begin, (end - begin) >> PAGE_SHIFT);
+ if (kernel_set_to_readonly) {
+ set_memory_nx(begin, (end - begin) >> PAGE_SHIFT);
+ set_memory_rw(begin, (end - begin) >> PAGE_SHIFT);
+ }
printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index a08a62c..5265335 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -778,6 +778,7 @@ void mark_rodata_ro(void)
unsigned long rodata_start =
((unsigned long)__start_rodata + PAGE_SIZE - 1) & PAGE_MASK;
unsigned long end = (unsigned long) &__end_rodata_hpage_align;
+ unsigned long kernel_end = (((unsigned long)&__init_end + HPAGE_SIZE) & HPAGE_MASK);
unsigned long text_end = PAGE_ALIGN((unsigned long) &__stop___ex_table);
unsigned long rodata_end = PAGE_ALIGN((unsigned long) &__end_rodata);
unsigned long data_start = (unsigned long) &_sdata;
@@ -788,11 +789,14 @@ void mark_rodata_ro(void)
kernel_set_to_readonly = 1;
+ /* make low level mapping NX */
+ set_memory_nx(PAGE_OFFSET, (PMD_PAGE_SIZE*PTRS_PER_PMD) >> PAGE_SHIFT);
+
/*
* The rodata section (but not the kernel text!) should also be
* not-executable.
*/
- set_memory_nx(rodata_start, (end - rodata_start) >> PAGE_SHIFT);
+ set_memory_nx(rodata_start, (kernel_end - rodata_start) >> PAGE_SHIFT);
rodata_test();
--
1.7.4.1
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