x86/boot/KASLR: Add checking for the offset of kernel virtual address randomization

For kernel text KASLR, the virtual address is confined to area of 1G,
[0xffffffff80000000, 0xffffffffc0000000). For the implemenataion of
virtual address randomization, we only randomize to get an offset
between 16M and 1G, then add this offset to the starting address,
0xffffffff80000000. Here 16M is the offset which is decided at linking
stage. So the amount of the local variable 'virt_addr' which respresents
the offset plus the kernel output size can not exceed KERNEL_IMAGE_SIZE.

Add a debug check for the offset. If out of bounds, print error
message and hang there.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Baoquan He <bhe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1498567146-11990-2-git-send-email-bhe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index b3c5a5f030ced9e6610aeb84889561a3a0f7500e..6008fa9b74d948ecbeb1193d3bf8973706ae7cec 100644 (file)
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -390,6 +390,8 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 #ifdef CONFIG_X86_64
        if (heap > 0x3fffffffffffUL)
                error("Destination address too large");
+       if (virt_addr + max(output_len, kernel_total_size) > KERNEL_IMAGE_SIZE)
+               error("Destination virtual address is beyond the kernel mapping area");
 #else
        if (heap > ((-__PAGE_OFFSET-(128<<20)-1) & 0x7fffffff))
                error("Destination address too large");