[PATCH] arm64: handle unmapped pages in initrd relocation

From: Mark Salter
Date: Mon Feb 01 2016 - 19:30:46 EST


Commit 4dffbfc48d65 ("arm64/efi: mark UEFI reserved regions as
MEMBLOCK_NOMAP") causes a potential problem in arm64 initrd relocation
code. If the kernel uses a pagesize greater than the 4k pagesize used
by UEFI, pagesize rounding may lead to one or both ends of the initrd
image to be marked unmapped. This leads to a panic when the kernel goes
to unpack it. This patch looks for unmapped pages at beginning and end
of the initrd image and if seen, relocated the initrd to a new area
completely covered by the kernel linear map.

Signed-off-by: Mark Salter <msalter@xxxxxxxxxx>
Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
arch/arm64/kernel/setup.c | 46 +++++++++++++++++++++++++++++++++++++---------
1 file changed, 37 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index d22c5fc..849566e 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -235,24 +235,29 @@ static void __init relocate_initrd(void)
phys_addr_t ram_end = memblock_end_of_DRAM();
phys_addr_t new_start;
unsigned long size, to_free = 0;
+ unsigned long unmapped_start = 0, unmapped_end = 0;
void *dest;

- if (orig_end <= ram_end)
+ size = orig_end - orig_start;
+ if (!size)
return;

/*
- * Any of the original initrd which overlaps the linear map should
- * be freed after relocating.
+ * If kernel pagesize > 4K, pagesize rounding may have placed
+ * part of either end of initrd in an unmapped page.
+ *
+ * Find any unmapped bytes at start or end of initrd.
*/
- if (orig_start < ram_end)
- to_free = ram_end - orig_start;
+ if (!memblock_is_map_memory(orig_start))
+ unmapped_start = PAGE_SIZE - (orig_start & (PAGE_SIZE - 1));
+ if (!memblock_is_map_memory(orig_end - 1))
+ unmapped_end = ((orig_end - 1) & (PAGE_SIZE - 1)) + 1;

- size = orig_end - orig_start;
- if (!size)
+ if (unmapped_start == 0 && unmapped_end == 0 && orig_end <= ram_end)
return;

/* initrd needs to be relocated completely inside linear mapping */
- new_start = memblock_find_in_range(0, PFN_PHYS(max_pfn),
+ new_start = memblock_find_in_range(0, ram_end,
size, PAGE_SIZE);
if (!new_start)
panic("Cannot relocate initrd of size %ld\n", size);
@@ -267,7 +272,30 @@ static void __init relocate_initrd(void)

dest = (void *)initrd_start;

- if (to_free) {
+ if (unmapped_end) {
+ copy_from_early_mem(dest + size - unmapped_end,
+ orig_start + size - unmapped_end,
+ unmapped_end);
+ size -= unmapped_end;
+ if (size == 0)
+ return;
+ }
+
+ if (unmapped_start) {
+ copy_from_early_mem(dest, orig_start, unmapped_start);
+ dest += unmapped_start;
+ orig_start += unmapped_start;
+ size -= unmapped_start;
+ if (size == 0)
+ return;
+ }
+
+ /*
+ * Any of the remaining original initrd which overlaps the linear map
+ * should be freed after relocating.
+ */
+ if (orig_start < ram_end) {
+ to_free = min(size, (unsigned long)(ram_end - orig_start));
memcpy(dest, (void *)__phys_to_virt(orig_start), to_free);
dest += to_free;
}
--
1.8.3.1