Commit 71179d5d authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Greg Kroah-Hartman

x86/bugs: Rework spec_ctrl base and mask logic

commit be6fcb54 upstream

x86_spec_ctrL_mask is intended to mask out bits from a MSR_SPEC_CTRL value
which are not to be modified. However the implementation is not really used
and the bitmask was inverted to make a check easier, which was removed in
"x86/bugs: Remove x86_spec_ctrl_set()"

Aside of that it is missing the STIBP bit if it is supported by the
platform, so if the mask would be used in x86_virt_spec_ctrl() then it
would prevent a guest from setting STIBP.

Add the STIBP bit if supported and use the mask in x86_virt_spec_ctrl() to
sanitize the value which is supplied by the guest.
Signed-off-by: default avatarThomas Gleixner <>
Reviewed-by: default avatarBorislav Petkov <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent d13f068b
......@@ -42,7 +42,7 @@ EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);
* The vendor and possibly platform specific bits which can be modified in
* x86_spec_ctrl_base.
static u64 __ro_after_init x86_spec_ctrl_mask = ~SPEC_CTRL_IBRS;
static u64 __ro_after_init x86_spec_ctrl_mask = SPEC_CTRL_IBRS;
* AMD specific MSR info for Speculative Store Bypass control.
......@@ -68,6 +68,10 @@ void __init check_bugs(void)
if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
/* Allow STIBP in MSR_SPEC_CTRL if supported */
if (boot_cpu_has(X86_FEATURE_STIBP))
x86_spec_ctrl_mask |= SPEC_CTRL_STIBP;
/* Select the proper spectre mitigation before patching alternatives */
......@@ -136,18 +140,26 @@ static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
u64 msrval, guestval, hostval = x86_spec_ctrl_base;
struct thread_info *ti = current_thread_info();
u64 msr, host = x86_spec_ctrl_base;
/* Is MSR_SPEC_CTRL implemented ? */
if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) {
* Restrict guest_spec_ctrl to supported values. Clear the
* modifiable bits in the host base value and or the
* modifiable bits from the guest value.
guestval = hostval & ~x86_spec_ctrl_mask;
guestval |= guest_spec_ctrl & x86_spec_ctrl_mask;
/* SSBD controlled in MSR_SPEC_CTRL */
if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD))
host |= ssbd_tif_to_spec_ctrl(ti->flags);
hostval |= ssbd_tif_to_spec_ctrl(ti->flags);
if (host != guest_spec_ctrl) {
msr = setguest ? guest_spec_ctrl : host;
wrmsrl(MSR_IA32_SPEC_CTRL, msr);
if (hostval != guestval) {
msrval = setguest ? guestval : hostval;
wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
......@@ -493,7 +505,7 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
switch (boot_cpu_data.x86_vendor) {
x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
x86_spec_ctrl_mask &= ~SPEC_CTRL_SSBD;
x86_spec_ctrl_mask |= SPEC_CTRL_SSBD;
wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
case X86_VENDOR_AMD:
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