[tip:x86/urgent] x86/boot/KASLR: Fix kexec crash due to 'virt_addr' calculation bug

[tip-bot for Baoquan He <tipbot@zytor.com>]

Commit-ID:  8eabf42ae5237e6b699aeac687b5b629e3537c8d
Gitweb:     http://git.kernel.org/tip/8eabf42ae5237e6b699aeac687b5b629e3537c8d
Author:     Baoquan He <bhe@redhat.com>
AuthorDate: Tue, 27 Jun 2017 20:39:06 +0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 30 Jun 2017 08:53:14 +0200

x86/boot/KASLR: Fix kexec crash due to 'virt_addr' calculation bug

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>
---
 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(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 54c24f0..56a7e92 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -564,9 +564,6 @@ void choose_random_location(unsigned long input,
 {
 	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;
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 6008fa9..00241c8 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -338,7 +338,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 				  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;
@@ -399,7 +399,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 #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
 
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 1c8355e..766a521 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -81,8 +81,6 @@ static inline void choose_random_location(unsigned long input,
 					  unsigned long output_size,
 					  unsigned long *virt_addr)
 {
-	/* No change from existing output location. */
-	*virt_addr = *output;
 }
 #endif