s390/kaslr: randomize amode31 base address

When the KASLR is enabled, randomize the base address of the amode31 image
within the first 2 GB, similar to the approach taken for the vmlinux
image. This makes it harder to predict the location of amode31 data
and code.

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index 638a6cf8a075b037d9897caa57c068717228749a..64bd7ac3e35d1beda4fa067b10e6f0828990bde1 100644 (file)
--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -278,7 +278,7 @@ void startup_kernel(void)
 {
        unsigned long max_physmem_end;
        unsigned long vmlinux_lma = 0;
-       unsigned long amode31_lma;
+       unsigned long amode31_lma = 0;
        unsigned long asce_limit;
        unsigned long safe_addr;
        void *img;
@@ -338,7 +338,9 @@ void startup_kernel(void)
 
        /* vmlinux decompression is done, shrink reserved low memory */
        physmem_reserve(RR_DECOMPRESSOR, 0, (unsigned long)_decompressor_end);
-       amode31_lma = vmlinux.default_lma - vmlinux.amode31_size;
+       if (kaslr_enabled())
+               amode31_lma = randomize_within_range(vmlinux.amode31_size, PAGE_SIZE, 0, SZ_2G);
+       amode31_lma = amode31_lma ?: vmlinux.default_lma - vmlinux.amode31_size;
        physmem_reserve(RR_AMODE31, amode31_lma, vmlinux.amode31_size);
 
        /*