When CONFIG_ARM64_RANDOMIZE_TEXT_OFFSET=y, we could end up with a
TEXT_OFFSET of less than 2 * PAGE_SIZE, which would result in an
overlap with the trampoline and a panic on boot.
Fix this by restricting the minimum value of the random TEXT_OFFSET
value so that it is not less than 2 pages when CONFIG_UNMAP_KERNEL_AT_EL0
is enabled.
I do wonder whether we should just remove
CONFIG_ARM64_RANDOMIZE_TEXT_OFFSET completely, since we're realistically
never going to be able to change our offset from 0x80000, but this keeps
the dream alive for now.
Signed-off-by: Will Deacon <will.dea...@arm.com>
---
arch/arm64/Makefile | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 939b310913cf..b60ac6c43ccd 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -87,9 +87,21 @@ head-y := arch/arm64/kernel/head.o
# The byte offset of the kernel image in RAM from the start of RAM.
ifeq ($(CONFIG_ARM64_RANDOMIZE_TEXT_OFFSET), y)
-TEXT_OFFSET := $(shell awk "BEGIN {srand(); printf \"0x%06x\n\", \
- int(2 * 1024 * 1024 / (2 ^ $(CONFIG_ARM64_PAGE_SHIFT)) * \
- rand()) * (2 ^ $(CONFIG_ARM64_PAGE_SHIFT))}")
+TEXT_OFFSET := $(shell awk
\
+ "BEGIN {
\
+ srand();
\
+ page_size = 2 ^ $(CONFIG_ARM64_PAGE_SHIFT);
\
+ tramp_size = 0;
\
+ if (\" $(CONFIG_UNMAP_KERNEL_AT_EL0)\" == \" y\") {
\
+ tramp_size = 2 * page_size;
\
+ }
\
+ offset = int(2 * 1024 * 1024 / page_size * rand());
\
+ offset *= page_size;
\
+ if (offset < tramp_size) {
\
+ offset = tramp_size;
\
+ }
\
+ printf \"0x%06x\n\", offset;
\
+ }")
else
TEXT_OFFSET := 0x00080000
endif
--
2.1.4
