Commit be6fcb54 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

x86/bugs: Rework spec_ctrl base and mask logic 



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 <tglx@linutronix.de>
Reviewed-by: default avatarBorislav Petkov <bp@suse.de>
parent 4b59bdb5

arch/x86/kernel/cpu/bugs.c

+19 −7
Original line number Diff line number Diff line
@@ -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 */

	spectre_v2_select_mitigation();
@@ -136,18 +140,26 @@ static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init = 
void

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) {

		case X86_VENDOR_INTEL:

			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);

			break;

		case X86_VENDOR_AMD:

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