[PATCH] arm64: handle unmapped pages in initrd relocation

[msalter@redhat.com (Mark Salter)]

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@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 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