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

Baoquan He
2014-09-12T06:22:44Z

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