The 'physmem' memblock table allows us to classify memory as RAM even
if it is not covered by the ordinary 'memory' memblock table.
Under CONFIG_STRICT_DEVMEM, we can use this to:
- allow read-only access to parts of RAM that are not considered memory
by the kernel, this is mainly intended for exposing UEFI configuration
tables such as SMBIOS to userland;
- avoid using non-cached mappings for those parts of RAM, as it may
result in mismatched attributes.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
arch/arm64/Kconfig | 1 +
arch/arm64/mm/mmap.c | 2 +-
arch/arm64/mm/mmu.c | 15 ++++++++++++++-
3 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b1f9a20a3677..86902f8d8e36 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -60,6 +60,7 @@ config ARM64
select HAVE_GENERIC_DMA_COHERENT
select HAVE_HW_BREAKPOINT if PERF_EVENTS
select HAVE_MEMBLOCK
+ select HAVE_MEMBLOCK_PHYS_MAP
select HAVE_PATA_PLATFORM
select HAVE_PERF_EVENTS
select HAVE_PERF_REGS
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 54922d1275b8..9f558ab41f39 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -126,7 +126,7 @@ 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 328638548871..083be3de1a87 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -122,7 +122,7 @@ 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 (!memblock_is_physmem(PFN_PHYS(pfn)))
return pgprot_noncached(vma_prot);
else if (file->f_flags & O_SYNC)
return pgprot_writecombine(vma_prot);
@@ -130,6 +130,19 @@ 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 system RAM */
+ if (memblock_is_physmem(PFN_PHYS(pfn)) && pgprot_val(*prot) & PTE_WRITE)
+ 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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