[Patch v2 1/2] kaslr: check if kernel location is changed

From: Baoquan He <bhe@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: kexec@lists.infradead.org, ebiederm@xmission.com, hpa@zytor.com,
	tglx@linutronix.de, mingo@redhat.com, vgoyal@redhat.com,
	keescook@chromium.org, ak@linux.intel.com,
	kumagai-atsushi@mxc.nes.nec.co.jp, Baoquan He <bhe@redhat.com>
Subject: [Patch v2 1/2] kaslr: check if kernel location is changed
Date: Fri, 12 Sep 2014 14:20:31 +0800	[thread overview]
Message-ID: <1410502832-3573-1-git-send-email-bhe@redhat.com> (raw)

Function handle_relocations() is used to do the relocations handling
for i686 and kaslr of x86_64. For 32 bit the relocation handling is
mandotary to perform. For x86_64 only when kaslr is enabled and a
random kernel location is chosen successfully the relocation handling
shound be done. However previous implementation only compared the
kernel loading address and LOAD_PHYSICAL_ADDR where kernel were
compiled to run at. This would casue system to hang when kernel
loading address is not equal to LOAD_PHYSICAL_ADDR.

So in this patch check if kernel location is changed after
choose_kernel_location() when x86_64. If and only if in x86_64
and kernel location is changed, we say a kaslr random kernel
location is chosen, then the relocation handling need be done.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 arch/x86/boot/compressed/misc.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 57ab74d..3bb2a17 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -230,8 +230,9 @@ static void error(char *x)
 		asm("hlt");
 }
 
-#if CONFIG_X86_NEED_RELOCS
-static void handle_relocations(void *output, unsigned long output_len)
+#ifdef CONFIG_X86_NEED_RELOCS
+static void handle_relocations(void *output_orig, void *output,
+			       unsigned long output_len)
 {
 	int *reloc;
 	unsigned long delta, map, ptr;
@@ -239,6 +240,20 @@ static void handle_relocations(void *output, unsigned long output_len)
 	unsigned long max_addr = min_addr + output_len;
 
 	/*
+	* 32bit always requires relocations to be performed. For x86_64,
+	* relocations need to be performed only if kaslr has chosen a
+	* different load address then kernel was originally loaded at.
+	*
+	* If we are here, either kaslr is not configured in or kaslr is disabled
+	* or kaslr has chosen not to change the load location of kernel. Don't
+	* perform any relocations.
+	*/
+#if CONFIG_X86_64
+	if (output_orig == output)
+		return;
+#endif
+
+	/*
 	 * Calculate the delta between where vmlinux was linked to load
 	 * and where it was actually loaded.
 	 */
@@ -299,7 +314,8 @@ static void handle_relocations(void *output, unsigned long output_len)
 #endif
 }
 #else
-static inline void handle_relocations(void *output, unsigned long output_len)
+static inline void handle_relocations(void *output_orig, void *output,
+				      unsigned long output_len)
 { }
 #endif
 
@@ -360,6 +376,8 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
 				  unsigned char *output,
 				  unsigned long output_len)
 {
+	unsigned char *output_orig = output;
+
 	real_mode = rmode;
 
 	sanitize_boot_params(real_mode);
@@ -402,7 +420,7 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
 	debug_putstr("\nDecompressing Linux... ");
 	decompress(input_data, input_len, NULL, NULL, output, NULL, error);
 	parse_elf(output);
-	handle_relocations(output, output_len);
+	handle_relocations(output_orig, output, output_len);
 	debug_putstr("done.\nBooting the kernel.\n");
 	return output;
 }
-- 
1.8.5.3

