diff options
| author | Russell King <rmk+kernel@arm.linux.org.uk> | 2015-08-19 20:40:41 +0100 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2015-08-26 20:34:24 +0100 |
| commit | a5e090acbf545c0a3b04080f8a488b17ec41fe02 (patch) | |
| tree | ae603e2e67bcac0564b2eba0a7771f8c5cebf352 /arch/arm/kernel/swp_emulate.c | |
| parent | 2190fed67ba6f3e8129513929f2395843645e928 (diff) | |
ARM: software-based priviledged-no-access support
Provide a software-based implementation of the priviledged no access
support found in ARMv8.1.
Userspace pages are mapped using a different domain number from the
kernel and IO mappings. If we switch the user domain to "no access"
when we enter the kernel, we can prevent the kernel from touching
userspace.
However, the kernel needs to be able to access userspace via the
various user accessor functions. With the wrapping in the previous
patch, we can temporarily enable access when the kernel needs user
access, and re-disable it afterwards.
This allows us to trap non-intended accesses to userspace, eg, caused
by an inadvertent dereference of the LIST_POISON* values, which, with
appropriate user mappings setup, can be made to succeed. This in turn
can allow use-after-free bugs to be further exploited than would
otherwise be possible.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/kernel/swp_emulate.c')
| -rw-r--r-- | arch/arm/kernel/swp_emulate.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c index 1361756782c7..5b26e7efa9ea 100644 --- a/arch/arm/kernel/swp_emulate.c +++ b/arch/arm/kernel/swp_emulate.c @@ -141,11 +141,14 @@ static int emulate_swpX(unsigned int address, unsigned int *data, while (1) { unsigned long temp; + unsigned int __ua_flags; + __ua_flags = uaccess_save_and_enable(); if (type == TYPE_SWPB) __user_swpb_asm(*data, address, res, temp); else __user_swp_asm(*data, address, res, temp); + uaccess_restore(__ua_flags); if (likely(res != -EAGAIN) || signal_pending(current)) break; |