mirror of
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2025-08-05 16:54:27 +00:00
890274c2dc
Kernel Userspace Access Prevention utilises a feature of the Radix MMU
which disallows read and write access to userspace addresses. By
utilising this, the kernel is prevented from accessing user data from
outside of trusted paths that perform proper safety checks, such as
copy_{to/from}_user() and friends.
Userspace access is disabled from early boot and is only enabled when
performing an operation like copy_{to/from}_user(). The register that
controls this (AMR) does not prevent userspace from accessing itself,
so there is no need to save and restore when entering and exiting
userspace.
When entering the kernel from the kernel we save AMR and if it is not
blocking user access (because eg. we faulted doing a user access) we
reblock user access for the duration of the exception (ie. the page
fault) and then restore the AMR when returning back to the kernel.
This feature can be tested by using the lkdtm driver (CONFIG_LKDTM=y)
and performing the following:
# (echo ACCESS_USERSPACE) > [debugfs]/provoke-crash/DIRECT
If enabled, this should send SIGSEGV to the thread.
We also add paranoid checking of AMR in switch and syscall return
under CONFIG_PPC_KUAP_DEBUG.
Co-authored-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
53 lines
1.3 KiB
C
53 lines
1.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
#ifndef _ASM_POWERPC_KUP_H_
|
|
#define _ASM_POWERPC_KUP_H_
|
|
|
|
#ifdef CONFIG_PPC64
|
|
#include <asm/book3s/64/kup-radix.h>
|
|
#endif
|
|
|
|
#ifndef __ASSEMBLY__
|
|
|
|
#include <asm/pgtable.h>
|
|
|
|
void setup_kup(void);
|
|
|
|
#ifdef CONFIG_PPC_KUEP
|
|
void setup_kuep(bool disabled);
|
|
#else
|
|
static inline void setup_kuep(bool disabled) { }
|
|
#endif /* CONFIG_PPC_KUEP */
|
|
|
|
#ifdef CONFIG_PPC_KUAP
|
|
void setup_kuap(bool disabled);
|
|
#else
|
|
static inline void setup_kuap(bool disabled) { }
|
|
static inline void allow_user_access(void __user *to, const void __user *from,
|
|
unsigned long size) { }
|
|
static inline void prevent_user_access(void __user *to, const void __user *from,
|
|
unsigned long size) { }
|
|
#endif /* CONFIG_PPC_KUAP */
|
|
|
|
static inline void allow_read_from_user(const void __user *from, unsigned long size)
|
|
{
|
|
allow_user_access(NULL, from, size);
|
|
}
|
|
|
|
static inline void allow_write_to_user(void __user *to, unsigned long size)
|
|
{
|
|
allow_user_access(to, NULL, size);
|
|
}
|
|
|
|
static inline void prevent_read_from_user(const void __user *from, unsigned long size)
|
|
{
|
|
prevent_user_access(NULL, from, size);
|
|
}
|
|
|
|
static inline void prevent_write_to_user(void __user *to, unsigned long size)
|
|
{
|
|
prevent_user_access(to, NULL, size);
|
|
}
|
|
|
|
#endif /* !__ASSEMBLY__ */
|
|
|
|
#endif /* _ASM_POWERPC_KUP_H_ */
|