linux-kernel - [PATCH v2 2/2] x86/boot/KASLR: Fix the wrong assignment to 'virt

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Date:   Tue, 27 Jun 2017 20:39:06 +0800
From:   Baoquan He <bhe@...hat.com>
To:     mingo@...nel.org, linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, hpa@...or.com, Baoquan He <bhe@...hat.com>
Subject: [PATCH v2 2/2] x86/boot/KASLR: Fix the wrong assignment to 'virt_addr'

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'. It's a code
bug.

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

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

Fixes: 8391c73 ("x86/KASLR: Randomize virtual address separately")
Tested-by: Dave Young <dyoung@...hat.com>
Signed-off-by: Baoquan He <bhe@...hat.com>
---
 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 fe318b44f7b8..91f27ab970ef 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -625,9 +625,6 @@ 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 6008fa9b74d9..00241c815524 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 1c8355eadbd1..766a5211f827 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
 
-- 
2.5.5