[PATCH 4.9 152/172] x86/boot/KASLR: Fix kexec crash due to virt_addr calculation bug

Greg Kroah-Hartman
2017-07-03T13:35:32Z

From: Baoquan He <bhe@redhat.com>

commit 8eabf42ae5237e6b699aeac687b5b629e3537c8d upstream.

Kernel text KASLR is separated into physical address and virtual
address randomization. And for virtual address randomization, we
only randomiza to get an offset between 16M and KERNEL_IMAGE_SIZE.
So the initial value of 'virt_addr' should be LOAD_PHYSICAL_ADDR,
but not the original kernel loading address 'output'.

The bug will cause kernel boot failure if kernel is loaded at a different
position than the address, 16M, which is decided at compiled time.
Kexec/kdump is such practical case.

To fix it, just assign LOAD_PHYSICAL_ADDR to virt_addr as initial
value.

Tested-by: Dave Young <dyoung@redhat.com>
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>
Fixes: 8391c73 ("x86/KASLR: Randomize virtual address separately")
Link: http://lkml.kernel.org/r/1498567146-11990-3-git-send-email-bhe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/boot/compressed/kaslr.c | 3 ---
arch/x86/boot/compressed/misc.c | 4 ++--
arch/x86/boot/compressed/misc.h | 2 --
3 files changed, 2 insertions(+), 7 deletions(-)

--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -430,9 +430,6 @@ void choose_random_location(unsigned lon
{
unsigned long random_addr, min_addr;

- /* By default, keep output position unchanged. */
- *virt_addr = *output;
-
if (cmdline_find_option_bool("nokaslr")) {
warn("KASLR disabled: 'nokaslr' on cmdline.");
return;
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -338,7 +338,7 @@ asmlinkage __visible void *extract_kerne
unsigned long output_len)
{
const unsigned long kernel_total_size = VO__end - VO__text;
- unsigned long virt_addr = (unsigned long)output;
+ unsigned long virt_addr = LOAD_PHYSICAL_ADDR;

/* Retain x86 boot parameters pointer passed from startup_32/64. */
boot_params = rmode;
@@ -397,7 +397,7 @@ asmlinkage __visible void *extract_kerne
#ifndef CONFIG_RELOCATABLE
if ((unsigned long)output != LOAD_PHYSICAL_ADDR)
error("Destination address does not match LOAD_PHYSICAL_ADDR");
- if ((unsigned long)output != virt_addr)
+ if (virt_addr != LOAD_PHYSICAL_ADDR)
error("Destination virtual address changed when not relocatable");
#endif

--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -81,8 +81,6 @@ static inline void choose_random_locatio
unsigned long output_size,
unsigned long *virt_addr)
{
- /* No change from existing output location. */
- *virt_addr = *output;
}
#endif