Commit 8391c73c authored by Baoquan He's avatar Baoquan He Committed by Ingo Molnar

x86/KASLR: Randomize virtual address separately

The current KASLR implementation randomizes the physical and virtual
addresses of the kernel together (both are offset by the same amount). It
calculates the delta of the physical address where vmlinux was linked
to load and where it is finally loaded. If the delta is not equal to 0
(i.e. the kernel was relocated), relocation handling needs be done.

On 64-bit, this patch randomizes both the physical address where kernel
is decompressed and the virtual address where kernel text is mapped and
will execute from. We now have two values being chosen, so the function
arguments are reorganized to pass by pointer so they can be directly
updated. Since relocation handling only depends on the virtual address,
we must check the virtual delta, not the physical delta for processing
kernel relocations. This also populates the page table for the new
virtual address range. 32-bit does not support a separate virtual address,
so it continues to use the physical offset for its virtual offset.

Additionally updates the sanity checks done on the resulting kernel
addresses since they are potentially separate now.

[kees: rewrote changelog, limited virtual split to 64-bit only, update checks]
[kees: fix CONFIG_RANDOMIZE_BASE=n boot failure]
Signed-off-by: default avatarBaoquan He <bhe@redhat.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: H.J. Lu <hjl.tools@gmail.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1464216334-17200-4-git-send-email-keescook@chromium.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 11fdf97a
...@@ -463,17 +463,20 @@ static unsigned long find_random_virt_addr(unsigned long minimum, ...@@ -463,17 +463,20 @@ static unsigned long find_random_virt_addr(unsigned long minimum,
* Since this function examines addresses much more numerically, * Since this function examines addresses much more numerically,
* it takes the input and output pointers as 'unsigned long'. * it takes the input and output pointers as 'unsigned long'.
*/ */
unsigned char *choose_random_location(unsigned long input, void choose_random_location(unsigned long input,
unsigned long input_size, unsigned long input_size,
unsigned long output, unsigned long *output,
unsigned long output_size) unsigned long output_size,
unsigned long *virt_addr)
{ {
unsigned long choice = output;
unsigned long random_addr; unsigned long random_addr;
/* By default, keep output position unchanged. */
*virt_addr = *output;
if (cmdline_find_option_bool("nokaslr")) { if (cmdline_find_option_bool("nokaslr")) {
warn("KASLR disabled: 'nokaslr' on cmdline."); warn("KASLR disabled: 'nokaslr' on cmdline.");
goto out; return;
} }
boot_params->hdr.loadflags |= KASLR_FLAG; boot_params->hdr.loadflags |= KASLR_FLAG;
...@@ -482,25 +485,25 @@ unsigned char *choose_random_location(unsigned long input, ...@@ -482,25 +485,25 @@ unsigned char *choose_random_location(unsigned long input,
initialize_identity_maps(); initialize_identity_maps();
/* Record the various known unsafe memory ranges. */ /* Record the various known unsafe memory ranges. */
mem_avoid_init(input, input_size, output); mem_avoid_init(input, input_size, *output);
/* Walk e820 and find a random address. */ /* Walk e820 and find a random address. */
random_addr = find_random_phys_addr(output, output_size); random_addr = find_random_phys_addr(*output, output_size);
if (!random_addr) { if (!random_addr) {
warn("KASLR disabled: could not find suitable E820 region!"); warn("KASLR disabled: could not find suitable E820 region!");
goto out; } else {
/* Update the new physical address location. */
if (*output != random_addr) {
add_identity_map(random_addr, output_size);
*output = random_addr;
}
} }
/* Always enforce the minimum. */
if (random_addr < choice)
goto out;
choice = random_addr;
add_identity_map(choice, output_size);
/* This actually loads the identity pagetable on x86_64. */ /* This actually loads the identity pagetable on x86_64. */
finalize_identity_maps(); finalize_identity_maps();
out:
return (unsigned char *)choice; /* Pick random virtual address starting from LOAD_PHYSICAL_ADDR. */
if (IS_ENABLED(CONFIG_X86_64))
random_addr = find_random_virt_addr(LOAD_PHYSICAL_ADDR, output_size);
*virt_addr = random_addr;
} }
...@@ -170,7 +170,8 @@ void __puthex(unsigned long value) ...@@ -170,7 +170,8 @@ void __puthex(unsigned long value)
} }
#if CONFIG_X86_NEED_RELOCS #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,
unsigned long virt_addr)
{ {
int *reloc; int *reloc;
unsigned long delta, map, ptr; unsigned long delta, map, ptr;
...@@ -182,11 +183,6 @@ static void handle_relocations(void *output, unsigned long output_len) ...@@ -182,11 +183,6 @@ static void handle_relocations(void *output, unsigned long output_len)
* and where it was actually loaded. * and where it was actually loaded.
*/ */
delta = min_addr - LOAD_PHYSICAL_ADDR; 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 * The kernel contains a table of relocation addresses. Those
...@@ -197,6 +193,20 @@ static void handle_relocations(void *output, unsigned long output_len) ...@@ -197,6 +193,20 @@ static void handle_relocations(void *output, unsigned long output_len)
*/ */
map = delta - __START_KERNEL_map; map = delta - __START_KERNEL_map;
/*
* 32-bit always performs relocations. 64-bit relocations are only
* needed if KASLR has chosen a different starting address offset
* from __START_KERNEL_map.
*/
if (IS_ENABLED(CONFIG_X86_64))
delta = virt_addr - 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. * Process relocations: 32 bit relocations first then 64 bit after.
* Three sets of binary relocations are added to the end of the kernel * Three sets of binary relocations are added to the end of the kernel
...@@ -250,7 +260,8 @@ static void handle_relocations(void *output, unsigned long output_len) ...@@ -250,7 +260,8 @@ static void handle_relocations(void *output, unsigned long output_len)
#endif #endif
} }
#else #else
static inline void handle_relocations(void *output, unsigned long output_len) static inline void handle_relocations(void *output, unsigned long output_len,
unsigned long virt_addr)
{ } { }
#endif #endif
...@@ -327,7 +338,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap, ...@@ -327,7 +338,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
unsigned long output_len) unsigned long output_len)
{ {
const unsigned long kernel_total_size = VO__end - VO__text; const unsigned long kernel_total_size = VO__end - VO__text;
unsigned char *output_orig = output; unsigned long virt_addr = (unsigned long)output;
/* Retain x86 boot parameters pointer passed from startup_32/64. */ /* Retain x86 boot parameters pointer passed from startup_32/64. */
boot_params = rmode; boot_params = rmode;
...@@ -366,13 +377,16 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap, ...@@ -366,13 +377,16 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
* the entire decompressed kernel plus relocation table, or the * the entire decompressed kernel plus relocation table, or the
* entire decompressed kernel plus .bss and .brk sections. * entire decompressed kernel plus .bss and .brk sections.
*/ */
output = choose_random_location((unsigned long)input_data, input_len, choose_random_location((unsigned long)input_data, input_len,
(unsigned long)output, (unsigned long *)&output,
max(output_len, kernel_total_size)); max(output_len, kernel_total_size),
&virt_addr);
/* Validate memory location choices. */ /* Validate memory location choices. */
if ((unsigned long)output & (MIN_KERNEL_ALIGN - 1)) if ((unsigned long)output & (MIN_KERNEL_ALIGN - 1))
error("Destination address inappropriately aligned"); error("Destination physical address inappropriately aligned");
if (virt_addr & (MIN_KERNEL_ALIGN - 1))
error("Destination virtual address inappropriately aligned");
#ifdef CONFIG_X86_64 #ifdef CONFIG_X86_64
if (heap > 0x3fffffffffffUL) if (heap > 0x3fffffffffffUL)
error("Destination address too large"); error("Destination address too large");
...@@ -382,19 +396,16 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap, ...@@ -382,19 +396,16 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
#endif #endif
#ifndef CONFIG_RELOCATABLE #ifndef CONFIG_RELOCATABLE
if ((unsigned long)output != LOAD_PHYSICAL_ADDR) if ((unsigned long)output != LOAD_PHYSICAL_ADDR)
error("Wrong destination address"); error("Destination address does not match LOAD_PHYSICAL_ADDR");
if ((unsigned long)output != virt_addr)
error("Destination virtual address changed when not relocatable");
#endif #endif
debug_putstr("\nDecompressing Linux... "); debug_putstr("\nDecompressing Linux... ");
__decompress(input_data, input_len, NULL, NULL, output, output_len, __decompress(input_data, input_len, NULL, NULL, output, output_len,
NULL, error); NULL, error);
parse_elf(output); parse_elf(output);
/* handle_relocations(output, output_len, virt_addr);
* 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);
debug_putstr("done.\nBooting the kernel.\n"); debug_putstr("done.\nBooting the kernel.\n");
return output; return output;
} }
...@@ -67,20 +67,22 @@ int cmdline_find_option_bool(const char *option); ...@@ -67,20 +67,22 @@ int cmdline_find_option_bool(const char *option);
#if CONFIG_RANDOMIZE_BASE #if CONFIG_RANDOMIZE_BASE
/* kaslr.c */ /* kaslr.c */
unsigned char *choose_random_location(unsigned long input_ptr, void choose_random_location(unsigned long input,
unsigned long input_size, unsigned long input_size,
unsigned long output_ptr, unsigned long *output,
unsigned long output_size); unsigned long output_size,
unsigned long *virt_addr);
/* cpuflags.c */ /* cpuflags.c */
bool has_cpuflag(int flag); bool has_cpuflag(int flag);
#else #else
static inline static inline void choose_random_location(unsigned long input,
unsigned char *choose_random_location(unsigned long input_ptr, unsigned long input_size,
unsigned long input_size, unsigned long *output,
unsigned long output_ptr, unsigned long output_size,
unsigned long output_size) unsigned long *virt_addr)
{ {
return (unsigned char *)output_ptr; /* No change from existing output location. */
*virt_addr = *output;
} }
#endif #endif
......
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