[PATCH v2] arm64: kaslr: Fix up the kernel image alignment

[Srinivas Ramana]

From: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>

If kernel image extends across alignment boundary, existing
code increases the KASLR offset by size of kernel image. The
offset is masked after resizing. There are cases, where after
masking, we may still have kernel image extending across
boundary. This eventually results in only 2MB block getting
mapped while creating the page tables. This results in data aborts
while accessing unmapped regions during second relocation (with
kaslr offset) in __primary_switch. To fix this problem, round up the
kernel image size, by swapper block size, before adding it for
correction.

For example consider below case, where kernel image still crosses
1GB alignment boundary, after masking the offset, which is fixed
by rounding up kernel image size.

SWAPPER_TABLE_SHIFT = 30
Swapper using section maps with section size 2MB.
CONFIG_PGTABLE_LEVELS = 3
VA_BITS = 39

_text  : 0xffffff8008080000
_end   : 0xffffff800aa1b000
offset : 0x1f35600000
mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1)

(_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7c
(_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d

offset after existing correction (before mask) = 0x1f37f9b000
(_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d
(_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d

offset (after mask) = 0x1f37e00000
(_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7c
(_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d

new offset w/ rounding up = 0x1f38000000
(_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d
(_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d

Fixes: f80fb3a3d508 ("arm64: add support for kernel ASLR")
Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Signed-off-by: Srinivas Ramana <sramana@xxxxxxxxxxxxxx>
---
 arch/arm64/kernel/kaslr.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 769f24ef628c..d7e90d97f5c4 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -131,11 +131,15 @@ u64 __init kaslr_early_init(u64 dt_phys, u64 modulo_offset)
 	/*
 	 * The kernel Image should not extend across a 1GB/32MB/512MB alignment
 	 * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this
-	 * happens, increase the KASLR offset by the size of the kernel image.
+	 * happens, increase the KASLR offset by the size of the kernel image
+	 * rounded up by SWAPPER_BLOCK_SIZE.
 	 */
 	if ((((u64)_text + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT) !=
-	    (((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT))
-		offset = (offset + (u64)(_end - _text)) & mask;
+	    (((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT)) {
+		u64 kimg_sz = _end - _text;
+		offset = (offset + round_up(kimg_sz, SWAPPER_BLOCK_SIZE))
+				& mask;
+	}
 
 	if (IS_ENABLED(CONFIG_KASAN))
 		/*
-- 
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