x86/IBRS: Make sure we restore MSR_IA32_SPEC_CTRL to a valid value

It is possible to (re-)enable IBRS between invocations of
ENABLE_IBRS_SAVE_AND_CLOBBER and RESTORE_IBRS_CLOBBER. If that happens,
the latter will be trying to write MSR_IA32_SPEC_CTRL with an
uninitialized value, possibly triggering a #GPF.

To avoid this let's make sure that we always save a valid value into
the save register. If IBRS is disabled that safe value will be
SPEC_CTRL_FEATURE_ENABLE_IBRS.

Orabug: 27378102

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
v2: Instead of setting to zero we set it to SPEC_CTRL_FEATURE_ENABLE_IBRS

Signed-off-by: Brian Maly <brian.maly@oracle.com>
Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>

diff --git a/arch/x86/include/asm/spec_ctrl.h b/arch/x86/include/asm/spec_ctrl.h
index 6cce513f3fb27b651e5a4c0372da8c4c1e1d8134..e62ea4685a1c20cba0a23f23d34fffaed59571d0 100644 (file)
--- a/arch/x86/include/asm/spec_ctrl.h
+++ b/arch/x86/include/asm/spec_ctrl.h
@@ -160,6 +160,7 @@
        wrmsr
        jmp 22f
 12:
+       movl $SPEC_CTRL_FEATURE_ENABLE_IBRS, \save_reg
        lfence
 22:
 .endm