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LoongArch: Add RANDOMIZE_KSTACK_OFFSET support

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Add support of kernel stack offset randomization while handling syscall,
the offset is defaultly limited by KSTACK_OFFSET_MAX().

In order to avoid triggering stack canaries (due to __builtin_alloca())
and slowing down the entry path, use __no_stack_protector attribute to
disable stack protector for do_syscall() at function level.

With this patch, the REPORT_STACK test show that:

	`loongarch64 bits of stack entropy: 7`

Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
This commit is contained in:
Jinjie Ruan 2024-07-20 22:40:58 +08:00 committed by Huacai Chen
parent 08f417db70
commit a0f7085f6a
2 changed files with 22 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

1
arch/loongarch/Kconfig
View file

@ -106,6 +106,7 @@ config LOONGARCH
select HAVE_ARCH_KFENCE
select HAVE_ARCH_KGDB if PERF_EVENTS
select HAVE_ARCH_MMAP_RND_BITS if MMU
select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
select HAVE_ARCH_SECCOMP
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK

22
arch/loongarch/kernel/syscall.c
View file

@ -9,11 +9,14 @@
#include <linux/entry-common.h>
#include <linux/errno.h>
#include <linux/linkage.h>
#include <linux/objtool.h>
#include <linux/randomize_kstack.h>
#include <linux/syscalls.h>
#include <linux/unistd.h>
#include <asm/asm.h>
#include <asm/exception.h>
#include <asm/loongarch.h>
#include <asm/signal.h>
#include <asm/switch_to.h>
#include <asm-generic/syscalls.h>
@ -39,7 +42,7 @@ void *sys_call_table[__NR_syscalls] = {
typedef long (*sys_call_fn)(unsigned long, unsigned long,
unsigned long, unsigned long, unsigned long, unsigned long);
void noinstr do_syscall(struct pt_regs *regs)
void noinstr __no_stack_protector do_syscall(struct pt_regs *regs)
{
unsigned long nr;
sys_call_fn syscall_fn;
@ -55,11 +58,28 @@ void noinstr do_syscall(struct pt_regs *regs)
nr = syscall_enter_from_user_mode(regs, nr);
add_random_kstack_offset();
if (nr < NR_syscalls) {
syscall_fn = sys_call_table[nr];
regs->regs[4] = syscall_fn(regs->orig_a0, regs->regs[5], regs->regs[6],
regs->regs[7], regs->regs[8], regs->regs[9]);
}
/*
* This value will get limited by KSTACK_OFFSET_MAX(), which is 10
* bits. The actual entropy will be further reduced by the compiler
* when applying stack alignment constraints: 16-bytes (i.e. 4-bits)
* aligned, which will remove the 4 low bits from any entropy chosen
* here.
*
* The resulting 6 bits of entropy is seen in SP[9:4].
*/
choose_random_kstack_offset(drdtime());
syscall_exit_to_user_mode(regs);
}
#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET
STACK_FRAME_NON_STANDARD(do_syscall);
#endif