diff options
| author | Chang S. Bae | 2020-05-28 16:13:57 -0400 |
|---|---|---|
| committer | Thomas Gleixner | 2020-06-18 15:47:04 +0200 |
| commit | c82965f9e53005c1c62632c468968293262056cb (patch) | |
| tree | 3652a3a69a88aaa2be261be10c02202c1e74a3ce /arch/x86/entry/calling.h | |
| parent | eaad981291ee36efee15a5e515d4598ae94ace07 (diff) | |
x86/entry/64: Handle FSGSBASE enabled paranoid entry/exit
Without FSGSBASE, user space cannot change GSBASE other than through a
PRCTL. The kernel enforces that the user space GSBASE value is postive as
negative values are used for detecting the kernel space GSBASE value in the
paranoid entry code.
If FSGSBASE is enabled, user space can set arbitrary GSBASE values without
kernel intervention, including negative ones, which breaks the paranoid
entry assumptions.
To avoid this, paranoid entry needs to unconditionally save the current
GSBASE value independent of the interrupted context, retrieve and write the
kernel GSBASE and unconditionally restore the saved value on exit. The
restore happens either in paranoid_exit or in the special exit path of the
NMI low level code.
All other entry code pathes which use unconditional SWAPGS are not affected
as they do not depend on the actual content.
[ tglx: Massaged changelogs and comments ]
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1557309753-24073-13-git-send-email-chang.seok.bae@intel.com
Link: https://lkml.kernel.org/r/20200528201402.1708239-12-sashal@kernel.org
Diffstat (limited to 'arch/x86/entry/calling.h')
| -rw-r--r-- | arch/x86/entry/calling.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h index 5c0cbb443030..98e4d8886f11 100644 --- a/arch/x86/entry/calling.h +++ b/arch/x86/entry/calling.h @@ -342,6 +342,12 @@ For 32-bit we have the following conventions - kernel is built with #endif .endm +.macro SAVE_AND_SET_GSBASE scratch_reg:req save_reg:req + rdgsbase \save_reg + GET_PERCPU_BASE \scratch_reg + wrgsbase \scratch_reg +.endm + #else /* CONFIG_X86_64 */ # undef UNWIND_HINT_IRET_REGS # define UNWIND_HINT_IRET_REGS |