Improve the handling of /dev/mem mappings under CONFIG_STRICT_DEVMEM by: - allowing read-only access to parts of System RAM that are not considered memory by the kernel, this is mainly intended for exposing UEFI Configuration tables to userland; - avoid using non-cached mappings for those parts of System RAM, as it may result in mismatched attributes.
Signed-off-by: Ard Biesheuvel <[email protected]> --- arch/arm64/mm/mmap.c | 5 +++-- arch/arm64/mm/mmu.c | 15 ++++++++++++++- 2 files changed, 17 insertions(+), 3 deletions(-) diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c index 1d73662f00ff..802cdf0df921 100644 --- a/arch/arm64/mm/mmap.c +++ b/arch/arm64/mm/mmap.c @@ -127,14 +127,15 @@ int valid_mmap_phys_addr_range(unsigned long pfn, size_t size) /* * devmem_is_allowed() checks to see if /dev/mem access to a certain address * is valid. The argument is a physical page number. We mimic x86 here by - * disallowing access to system RAM as well as device-exclusive MMIO regions. + * disallowing access to system RAM that is in active use by the kernel, as + * well as device-exclusive MMIO regions. * This effectively disable read()/write() on /dev/mem. */ int devmem_is_allowed(unsigned long pfn) { if (iomem_is_exclusive(pfn << PAGE_SHIFT)) return 0; - if (!page_is_ram(pfn)) + if (!pfn_valid(pfn)) return 1; return 0; } diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 4d583aa9ff4e..93ba10838359 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -121,7 +121,7 @@ early_param("cachepolicy", early_cachepolicy); pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn, unsigned long size, pgprot_t vma_prot) { - if (!pfn_valid(pfn)) + if (!page_is_ram(pfn)) return pgprot_noncached(vma_prot); else if (file->f_flags & O_SYNC) return pgprot_writecombine(vma_prot); @@ -129,6 +129,19 @@ pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn, } EXPORT_SYMBOL(phys_mem_access_prot); +/* + * This definition of phys_mem_access_prot_allowed() overrides + * the __weak definition in drivers/char/mem.c + */ +int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn, + unsigned long size, pgprot_t *prot) +{ + /* Disallow read-write access to reserved system RAM */ + if ((pgprot_val(*prot) & PTE_WRITE) && page_is_ram(pfn)) + return 0; + return 1; +} + static void __init *early_alloc(unsigned long sz) { void *ptr = __va(memblock_alloc(sz, sz)); -- 1.8.3.2 -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
