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 <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Dan Williams <[email protected]> --- 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.
