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Subject[PATCH 4.14 57/95] x86/bugs: Whitelist allowed SPEC_CTRL MSR values
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

commit 1115a859f33276fe8afb31c60cf9d8e657872558 upstream

Intel and AMD SPEC_CTRL (0x48) MSR semantics may differ in the
future (or in fact use different MSRs for the same functionality).

As such a run-time mechanism is required to whitelist the appropriate MSR
values.

[ tglx: Made the variable __ro_after_init ]

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/cpu/bugs.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -35,6 +35,12 @@ static void __init ssb_select_mitigation
*/
static u64 __ro_after_init 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;
+
void __init check_bugs(void)
{
identify_boot_cpu();
@@ -117,7 +123,7 @@ static enum spectre_v2_mitigation spectr

void x86_spec_ctrl_set(u64 val)
{
- if (val & ~(SPEC_CTRL_IBRS | SPEC_CTRL_RDS))
+ if (val & x86_spec_ctrl_mask)
WARN_ONCE(1, "SPEC_CTRL MSR value 0x%16llx is unknown.\n", val);
else
wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base | val);
@@ -459,6 +465,7 @@ static enum ssb_mitigation_cmd __init __
switch (boot_cpu_data.x86_vendor) {
case X86_VENDOR_INTEL:
x86_spec_ctrl_base |= SPEC_CTRL_RDS;
+ x86_spec_ctrl_mask &= ~SPEC_CTRL_RDS;
x86_spec_ctrl_set(SPEC_CTRL_RDS);
break;
case X86_VENDOR_AMD:
@@ -482,7 +489,7 @@ static void ssb_select_mitigation()
void x86_spec_ctrl_setup_ap(void)
{
if (boot_cpu_has(X86_FEATURE_IBRS))
- x86_spec_ctrl_set(x86_spec_ctrl_base & (SPEC_CTRL_IBRS | SPEC_CTRL_RDS));
+ x86_spec_ctrl_set(x86_spec_ctrl_base & ~x86_spec_ctrl_mask);
}

#ifdef CONFIG_SYSFS

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