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ARM: move signal handlers into a vdso-like page

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Move the signal handlers into a VDSO page rather than keeping them in
the vectors page.  This allows us to place them randomly within this
page, and also map the page at a random location within userspace
further protecting these code fragments from ROP attacks.  The new
VDSO page is also poisoned in the same way as the vector page.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Russell King
2013-07-24 00:29:18 +01:00
parent f6f91b0d9f
commit 48be69a026
6 changed files with 87 additions and 31 deletions
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52
arch/arm/kernel/signal.c
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@@ -8,6 +8,7 @@
* published by the Free Software Foundation.
*/
#include <linux/errno.h>
#include <linux/random.h>
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/uaccess.h>
@@ -15,12 +16,11 @@
#include <asm/elf.h>
#include <asm/cacheflush.h>
#include <asm/traps.h>
#include <asm/ucontext.h>
#include <asm/unistd.h>
#include <asm/vfp.h>
#include "signal.h"
/*
* For ARM syscalls, we encode the syscall number into the instruction.
*/
@@ -40,11 +40,13 @@
#define SWI_THUMB_SIGRETURN (0xdf00 << 16 | 0x2700 | (__NR_sigreturn - __NR_SYSCALL_BASE))
#define SWI_THUMB_RT_SIGRETURN (0xdf00 << 16 | 0x2700 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
const unsigned long sigreturn_codes[7] = {
static const unsigned long sigreturn_codes[7] = {
MOV_R7_NR_SIGRETURN, SWI_SYS_SIGRETURN, SWI_THUMB_SIGRETURN,
MOV_R7_NR_RT_SIGRETURN, SWI_SYS_RT_SIGRETURN, SWI_THUMB_RT_SIGRETURN,
};
static unsigned long signal_return_offset;
#ifdef CONFIG_CRUNCH
static int preserve_crunch_context(struct crunch_sigframe __user *frame)
{
@@ -401,12 +403,15 @@ setup_return(struct pt_regs *regs, struct ksignal *ksig,
return 1;
if ((cpsr & MODE32_BIT) && !IS_ENABLED(CONFIG_ARM_MPU)) {
struct mm_struct *mm = current->mm;
/*
* 32-bit code can use the new high-page
* signal return code support except when the MPU has
* protected the vectors page from PL0
* 32-bit code can use the signal return page
* except when the MPU has protected the vectors
* page from PL0
*/
retcode = KERN_SIGRETURN_CODE + (idx << 2) + thumb;
retcode = mm->context.sigpage + signal_return_offset +
(idx << 2) + thumb;
} else {
/*
* Ensure that the instruction cache sees
@@ -608,3 +613,36 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
} while (thread_flags & _TIF_WORK_MASK);
return 0;
}
static struct page *signal_page;
struct page *get_signal_page(void)
{
if (!signal_page) {
unsigned long ptr;
unsigned offset;
void *addr;
signal_page = alloc_pages(GFP_KERNEL, 0);
if (!signal_page)
return NULL;
addr = page_address(signal_page);
/* Give the signal return code some randomness */
offset = 0x200 + (get_random_int() & 0x7fc);
signal_return_offset = offset;
/*
* Copy signal return handlers into the vector page, and
* set sigreturn to be a pointer to these.
*/
memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
ptr = (unsigned long)addr + offset;
flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
}
return signal_page;
}