On 11/18/14 at 01:57pm, Ard Biesheuvel wrote:
> 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;
Ard, can you elabrate a bit? Are this for the acpi case because no dtb in
procfs?
Anyway I also think using /dev/mem looks not a good way to expose
infomation to userspace.
> - avoid using non-cached mappings for those parts of System RAM, as it
> may result in mismatched attributes.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
> 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
>
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