When FSGSBASE is enabled, GSBASE handling on the paranoid entry will need to retrieve the kernel GSBASE. Thus, the kernel page table should be in. As a preparation, the CR3 switching is moved to happen at first, before the SWAPGS.
Current GSBASE switching mechanism is possible without the kernel page table in. No functional change is expected. Signed-off-by: Chang S. Bae <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Andi Kleen <[email protected]> --- arch/x86/entry/entry_64.S | 29 +++++++++++++++++------------ 1 file changed, 17 insertions(+), 12 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 568a491..034d8f8 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1160,18 +1160,6 @@ ENTRY(paranoid_entry) PUSH_AND_CLEAR_REGS save_ret=1 ENCODE_FRAME_POINTER 8 - movl $1, %ebx - /* - * The kernel-enforced convention is a negative GSBASE indicates - * a kernel value. - */ - READ_MSR_GSBASE save_reg=%edx - testl %edx, %edx /* Negative -> in kernel */ - js 1f - SWAPGS - xorl %ebx, %ebx - -1: /* * Always stash CR3 in %r14. This value will be restored, * verbatim, at exit. Needed if paranoid_entry interrupted @@ -1181,9 +1169,26 @@ ENTRY(paranoid_entry) * This is also why CS (stashed in the "iret frame" by the * hardware at entry) can not be used: this may be a return * to kernel code, but with a user CR3 value. + * + * This PTI macro doesn't depend on kernel GSBASE and, with + * FSGSBASE, the GSBASE handling requires the kernel page + * tables switched in. So, do it early here. */ SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14 + movl $1, %ebx + /* + * The kernel-enforced convention is a negative GSBASE indicates + * a kernel value. + */ + READ_MSR_GSBASE save_reg=%edx + testl %edx, %edx /* Negative -> in kernel */ + jns .Lparanoid_entry_swapgs + ret + +.Lparanoid_entry_swapgs: + SWAPGS + xorl %ebx, %ebx ret END(paranoid_entry) -- 2.7.4
