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Subject[PATCH v2 9/9] change the relocations behavior for kaslr on x86_64
Date
On x86_64, in old kaslr implementaion only physical address of kernel
loading is randomized. Then calculate the delta of physical address
where vmlinux was linked to load and where it is finally loaded. If
delta is not equal to 0, namely there's a new physical address where
kernel is actually decompressed, relocation handling need be done. Then
delta is added to offset of kernel symbol relocation, this makes the
address of kernel text mapping move delta long.

Here the behavior is changed. Randomize both the physical address
where kernel is decompressed and the virtual address where kernel text
is mapped. And physical address can be randomized from where vmlinux
was linked to load to maximum physical memory, possibly near 64T. While
virtual address can get a random offset from load address to
CONFIG_RANDOMIZE_BASE_MAX_OFFSET, then added to __START_KERNEL_map.

And relocation handling only depends on virtual address randomization.
Means if and only if virtual address is randomized to a different value,
we add the delta to the offset of kernel relocs.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
arch/x86/boot/compressed/aslr.c | 29 ++++++++++++++---------------
arch/x86/boot/compressed/misc.c | 34 +++++++++++++++++++++-------------
arch/x86/boot/compressed/misc.h | 22 ++++++++++++----------
3 files changed, 47 insertions(+), 38 deletions(-)

diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index 332a8c4..3114ae0 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -426,13 +426,13 @@ static void add_kaslr_setup_data(struct boot_params *params, __u8 enabled)

}

-unsigned char *choose_kernel_location(struct boot_params *params,
- unsigned char *input,
- unsigned long input_size,
- unsigned char *output,
- unsigned long output_size)
+void choose_kernel_location(struct boot_params *params,
+ unsigned char *input,
+ unsigned long input_size,
+ unsigned char **output,
+ unsigned long output_size,
+ unsigned char **virt_offset)
{
- unsigned long choice = (unsigned long)output;
unsigned long random;

#ifdef CONFIG_HIBERNATION
@@ -455,17 +455,16 @@ unsigned char *choose_kernel_location(struct boot_params *params,
output_size);

/* Walk e820 and find a random address. */
- random = find_random_addr(choice, output_size);
- if (!random) {
+ random = find_random_phy_addr((unsigned long)*output, output_size);
+ if (!random)
debug_putstr("KASLR could not find suitable E820 region...\n");
- goto out;
- }
+ else
+ *output = (unsigned char*)random;

- /* Always enforce the minimum. */
- if (random < choice)
- goto out;
+ random = find_random_virt_offset(LOAD_PHYSICAL_ADDR, output_size);
+ *virt_offset = (unsigned char*)random;

- choice = random;
out:
- return (unsigned char *)choice;
+ if (!random)
+ *virt_offset = (unsigned char*)LOAD_PHYSICAL_ADDR;
}
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index c9d8187..53bb2dc 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -236,7 +236,8 @@ static void error(char *x)
}

#if CONFIG_X86_NEED_RELOCS
-static void handle_relocations(void *output, unsigned long output_len)
+static void handle_relocations(void *output, unsigned long output_len,
+ void *virt_offset)
{
int *reloc;
unsigned long delta, map, ptr;
@@ -248,11 +249,6 @@ static void handle_relocations(void *output, unsigned long output_len)
* and where it was actually loaded.
*/
delta = min_addr - LOAD_PHYSICAL_ADDR;
- if (!delta) {
- debug_putstr("No relocation needed... ");
- return;
- }
- debug_putstr("Performing relocations... ");

/*
* The kernel contains a table of relocation addresses. Those
@@ -263,6 +259,16 @@ static void handle_relocations(void *output, unsigned long output_len)
*/
map = delta - __START_KERNEL_map;

+ /* */
+ if (IS_ENABLED(CONFIG_X86_64))
+ delta = (unsigned long)virt_offset - LOAD_PHYSICAL_ADDR;
+
+ if (!delta) {
+ debug_putstr("No relocation needed... ");
+ return;
+ }
+ debug_putstr("Performing relocations... ");
+
/*
* Process relocations: 32 bit relocations first then 64 bit after.
* Three sets of binary relocations are added to the end of the kernel
@@ -316,7 +322,8 @@ 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, unsigned long output_len,
+ void *virt_offset)
{ }
#endif

@@ -381,6 +388,7 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
unsigned long run_size)
{
unsigned char *output_orig = output;
+ unsigned char * virt_offset;

real_mode = rmode;

@@ -408,10 +416,11 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
* the entire decompressed kernel plus relocation table, or the
* entire decompressed kernel plus .bss and .brk sections.
*/
- output = choose_kernel_location(real_mode, input_data, input_len,
- output,
- output_len > run_size ? output_len
- : run_size);
+ choose_kernel_location(real_mode, input_data, input_len,
+ &output,
+ output_len > run_size ? output_len
+ : run_size,
+ &virt_offset);

/* Validate memory location choices. */
if ((unsigned long)output & (MIN_KERNEL_ALIGN - 1))
@@ -438,8 +447,7 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
* 32-bit always performs relocations. 64-bit relocations are only
* needed if kASLR has chosen a different load address.
*/
- if (!IS_ENABLED(CONFIG_X86_64) || output != output_orig)
- handle_relocations(output, output_len);
+ handle_relocations(output, output_len, virt_offset);
debug_putstr("done.\nBooting the kernel.\n");
return output;
}
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index b901a8b..9da6b89 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -59,20 +59,22 @@ int cmdline_find_option_bool(const char *option);

#if CONFIG_RANDOMIZE_BASE
/* aslr.c */
-unsigned char *choose_kernel_location(struct boot_params *params,
- unsigned char *input,
- unsigned long input_size,
- unsigned char *output,
- unsigned long output_size);
+void choose_kernel_location(struct boot_params *params,
+ unsigned char *input,
+ unsigned long input_size,
+ unsigned char **output,
+ unsigned long output_size,
+ unsigned char **virt_offset);
/* cpuflags.c */
bool has_cpuflag(int flag);
#else
static inline
-unsigned char *choose_kernel_location(struct boot_params *params,
- unsigned char *input,
- unsigned long input_size,
- unsigned char *output,
- unsigned long output_size)
+void choose_kernel_location(struct boot_params *params,
+ unsigned char *input,
+ unsigned long input_size,
+ unsigned char *output,
+ unsigned long output_size,
+ unsigned char **virt_offset)
{
return output;
}
--
1.9.3


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