Changing devmem_is_allowed so that on an EFI machine, access to physical
address below 1 MB is allowed only to physical pages that are valid in
the EFI memory map. This prevents the possibility of an MCE due to
accessing an invalid physical address.
Signed-off-by: T Makphaibulchoke <t...@hp.com>
---
arch/x86/mm/init.c | 12 ++++++++++--
include/linux/mm.h | 1 +
kernel/resource.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 58 insertions(+), 2 deletions(-)
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index ab1f6a9..3ed95c5 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -4,6 +4,7 @@
#include <linux/swap.h>
#include <linux/memblock.h>
#include <linux/bootmem.h> /* for max_low_pfn */
+#include <linux/efi.h> /* for efi_enabled */
#include <asm/cacheflush.h>
#include <asm/e820.h>
@@ -319,8 +320,15 @@ unsigned long __init_refok init_memory_mapping(unsigned
long start,
*/
int devmem_is_allowed(unsigned long pagenr)
{
- if (pagenr < 256)
- return 1;
+ if (pagenr < 256) {
+ if (!efi_enabled)
+ return 1;
+ /* For EFI, allow access only to valid physical addresses. */
+ if (page_is_valid(pagenr))
+ return 1;
+ return 0;
+ }
+
if (iomem_is_exclusive(pagenr << PAGE_SHIFT))
return 0;
if (!page_is_ram(pagenr))
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 311be90..fd1bcd4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -288,6 +288,7 @@ static inline int get_page_unless_zero(struct page *page)
}
extern int page_is_ram(unsigned long pfn);
+extern int page_is_valid(unsigned long pfn);
/* Support for virtually mapped pages */
struct page *vmalloc_to_page(const void *addr);
diff --git a/kernel/resource.c b/kernel/resource.c
index 34d4588..aeb091b 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -367,6 +367,53 @@ int __weak page_is_ram(unsigned long pfn)
return walk_system_ram_range(pfn, 1, NULL, __is_ram) == 1;
}
+static int find_next_system_resource(struct resource *res)
+{
+ resource_size_t start, end;
+ struct resource *p;
+
+ BUG_ON(!res);
+
+ start = res->start;
+ end = res->end;
+ BUG_ON(start >= end);
+
+ read_lock(&resource_lock);
+ for (p = iomem_resource.child; p ; p = p->sibling) {
+ /* system ram is just marked as IORESOURCE_MEM */
+ if (!(p->flags & res->flags))
+ continue;
+ if (p->start > end) {
+ p = NULL;
+ break;
+ }
+ if ((p->end >= start) && (p->start < end))
+ break;
+ }
+ read_unlock(&resource_lock);
+ if (!p)
+ return -1;
+ /* copy data */
+ if (res->start < p->start)
+ res->start = p->start;
+ if (res->end > p->end)
+ res->end = p->end;
+ return 0;
+}
+
+int __weak page_is_valid(unsigned long start_pfn)
+{
+ struct resource res;
+ int ret = 0;
+
+ res.start = (u64) start_pfn << PAGE_SHIFT;
+ res.end = ((u64)(start_pfn + 1) << PAGE_SHIFT) - 1;
+ res.flags = IORESOURCE_MEM;
+ if (find_next_system_resource(&res) >= 0)
+ ret = 1;
+ return ret;
+}
+
void __weak arch_remove_reservations(struct resource *avail)
{
}
--
1.7.1
--
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