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 <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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