[PATCH] x86/mm: Add x86 valid_phys_addr_range() for /dev/mem

[Toshi Kani]

x86 does not define ARCH_HAS_VALID_PHYS_ADDR_RANGE, which
leads /dev/mem to use the default valid_phys_addr_range()
and valid_mmap_phys_addr_range() in drivers/char/mem.c.

The default valid_phys_addr_range() allows any range lower
than __pa(high_memory), which is the end of system RAM, and
disallows any range higher than it.

Persistent memory may be located at lower and/or higher
address of __pa(high_memory) depending on their memory slots.
When using crash(8) via /dev/mem for analyzing data in
persistent memory, it can only access to the one lower than
__pa(high_memory).

Add x86 valid_phys_addr_range() and valid_mmap_phys_addr_range()
to provide better checking:
 - Physical address range is valid when it is fully backed by
   IORESOURCE_MEM, regardless of __pa(high_memory).
 - Other ranges, including holes, are invalid.

This also allows crash(8) to access persistent memory ranges
via /dev/mem (with a minor change to remove high_memory check
from crash itself).

Note, /dev/mem makes additional check with devmem_is_allowed()
for read/write when CONFIG_STRICT_DEVMEM is set, and does always
for mmap.  CONFIG_IO_STRICT_DEVMEM provides further restriction.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
---
This patch applies on top of the patch-set below, and is based
on the tip tree.
https://lkml.org/lkml/2016/1/26/886
---
 arch/x86/include/asm/io.h |    3 +++
 arch/x86/mm/init.c        |   24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index de25aad..189901a 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -36,6 +36,7 @@
 
 #define ARCH_HAS_IOREMAP_WC
 #define ARCH_HAS_IOREMAP_WT
+#define ARCH_HAS_VALID_PHYS_ADDR_RANGE
 
 #include <linux/string.h>
 #include <linux/compiler.h>
@@ -326,6 +327,8 @@ extern void __iomem *ioremap_wc(resource_size_t offset, unsigned long size);
 extern void __iomem *ioremap_wt(resource_size_t offset, unsigned long size);
 
 extern bool is_early_ioremap_ptep(pte_t *ptep);
+extern int valid_phys_addr_range(phys_addr_t addr, size_t size);
+extern int valid_mmap_phys_addr_range(unsigned long pfn, size_t size);
 
 #ifdef CONFIG_XEN
 #include <xen/xen.h>
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 493f541..35cf96f 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -624,6 +624,30 @@ void __init init_mem_mapping(void)
 	early_memtest(0, max_pfn_mapped << PAGE_SHIFT);
 }
 
+/**
+ * valid_phys_addr_range - check phys addr for /dev/mem read and write
+ *
+ * Return true if a target physical address is marked as IORESOURCE_MEM.
+ */
+int valid_phys_addr_range(phys_addr_t addr, size_t size)
+{
+	return (region_intersects(addr, size, IORESOURCE_MEM,
+				  IORES_DESC_NONE) == REGION_INTERSECTS);
+}
+
+/**
+ * valid_mmap_phys_addr_range - check phys addr for /dev/mem mmap
+ *
+ * Return true if a target physical address is marked as IORESOURCE_MEM.
+ */
+int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
+{
+	resource_size_t addr = pfn << PAGE_SHIFT;
+
+	return (region_intersects(addr, size, IORESOURCE_MEM,
+				  IORES_DESC_NONE) == REGION_INTERSECTS);
+}
+
 /*
  * devmem_is_allowed() checks to see if /dev/mem access to a certain address
  * is valid. The argument is a physical page number.