The kernel sets the NX bit in the early page tables without checking whether
the CPU actually supports this feature. If it doesn't the first attempt to use
them will cause a kernel hang. Since these are temporary page tables marked as
initdata this fix takes the approach of not bothering with the NX bit at all.
Noticed when my AMD machine that happened to have the NX feature disabled by
the BIOS failed to boot after the update to 3.9.
Cc: [email protected]
Signed-off-by: Fernando Luis Vazquez Cao <[email protected]>
---
diff -urNp linux-3.9/arch/x86/kernel/head64.c linux-3.9-fix/arch/x86/kernel/head64.c
--- linux-3.9/arch/x86/kernel/head64.c 2013-04-29 09:36:01.000000000 +0900
+++ linux-3.9-fix/arch/x86/kernel/head64.c 2013-05-02 14:38:52.589276092 +0900
@@ -99,7 +99,7 @@ again:
pmd_p[i] = 0;
*pud_p = (pudval_t)pmd_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
}
- pmd = (physaddr & PMD_MASK) + (__PAGE_KERNEL_LARGE & ~_PAGE_GLOBAL);
+ pmd = (physaddr & PMD_MASK) + (__PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL);
pmd_p[pmd_index(address)] = pmd;
return 0;
Commit-ID: 78d77df71510a96e042de7ba6dbd7998103642cb
Gitweb: http://git.kernel.org/tip/78d77df71510a96e042de7ba6dbd7998103642cb
Author: H. Peter Anvin <[email protected]>
AuthorDate: Thu, 2 May 2013 10:33:46 -0700
Committer: H. Peter Anvin <[email protected]>
CommitDate: Thu, 2 May 2013 11:27:35 -0700
x86-64, init: Do not set NX bits on non-NX capable hardware
During early init, we would incorrectly set the NX bit even if the NX
feature was not supported. Instead, only set this bit if NX is
actually available and enabled. We already do very early detection of
the NX bit to enable it in EFER, this simply extends this detection to
the early page table mask.
Reported-by: Fernando Luis Vázquez Cao <[email protected]>
Signed-off-by: H. Peter Anvin <[email protected]>
Link: http://lkml.kernel.org/r/1367476850.5660.2.camel@nexus
Cc: <[email protected]> v3.9
---
arch/x86/kernel/head64.c | 3 ++-
arch/x86/kernel/head_64.S | 1 +
2 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 101ac1a9..dab95a8 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -34,6 +34,7 @@
extern pgd_t early_level4_pgt[PTRS_PER_PGD];
extern pmd_t early_dynamic_pgts[EARLY_DYNAMIC_PAGE_TABLES][PTRS_PER_PMD];
static unsigned int __initdata next_early_pgt = 2;
+pmdval_t __initdata early_pmd_flags = __PAGE_KERNEL_LARGE & ~(_PAGE_GLOBAL | _PAGE_NX);
/* Wipe all early page tables except for the kernel symbol map */
static void __init reset_early_page_tables(void)
@@ -99,7 +100,7 @@ again:
pmd_p[i] = 0;
*pud_p = (pudval_t)pmd_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
}
- pmd = (physaddr & PMD_MASK) + (__PAGE_KERNEL_LARGE & ~_PAGE_GLOBAL);
+ pmd = (physaddr & PMD_MASK) + early_pmd_flags;
pmd_p[pmd_index(address)] = pmd;
return 0;
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 6859e96..08f7e80 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -200,6 +200,7 @@ ENTRY(secondary_startup_64)
btl $20,%edi /* No Execute supported? */
jnc 1f
btsl $_EFER_NX, %eax
+ btsq $_PAGE_BIT_NX,early_pmd_flags(%rip)
1: wrmsr /* Make changes effective */
/* Setup cr0 */
(resending as plaintext)
> During early init, we would incorrectly set the NX bit even if the NX
> feature was not supported. Instead, only set this bit if NX is
> actually available and enabled. We already do very early detection of
> the NX bit to enable it in EFER, this simply extends this detection to
> the early page table mask.
AFAIK the only production x86-64 processor that don't support NX that I know of is the original Nocona D0 stepping.
Must more common are the problem of BIOSes disabling the NX feature.
Yuhong Bao -
Yes... But both apply.
Yuhong Bao <[email protected]> wrote:
>(resending as plaintext)
>> During early init, we would incorrectly set the NX bit even if the NX
>> feature was not supported. Instead, only set this bit if NX is
>> actually available and enabled. We already do very early detection
>of
>> the NX bit to enable it in EFER, this simply extends this detection
>to
>> the early page table mask.
>AFAIK the only production x86-64 processor that don't support NX that I
>know of is the original Nocona D0 stepping.
>Must more common are the problem of BIOSes disabling the NX feature.
>
>
>Yuhong Bao
--
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