Commit 87781880 authored by Borislav Petkov (AMD)'s avatar Borislav Petkov (AMD)
Browse files

x86/bugs: Add SRSO_USER_KERNEL_NO support 



If the machine has:

  CPUID Fn8000_0021_EAX[30] (SRSO_USER_KERNEL_NO) -- If this bit is 1,
  it indicates the CPU is not subject to the SRSO vulnerability across
  user/kernel boundaries.

have it fall back to IBPB on VMEXIT only, in the case it is going to run
VMs:

  Speculative Return Stack Overflow: Mitigation: IBPB on VMEXIT only

Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: default avatarNikolay Borisov <nik.borisov@suse.com>
Link: https://lore.kernel.org/r/20241202120416.6054-2-bp@kernel.org
parent fc033cf2

arch/x86/include/asm/cpufeatures.h

+1 −0
Original line number Diff line number Diff line
@@ -465,6 +465,7 @@ 
#define X86_FEATURE_SBPB		(20*32+27) /* Selective Branch Prediction Barrier */

#define X86_FEATURE_IBPB_BRTYPE		(20*32+28) /* MSR_PRED_CMD[IBPB] flushes all branch type predictions */

#define X86_FEATURE_SRSO_NO		(20*32+29) /* CPU is not affected by SRSO */

#define X86_FEATURE_SRSO_USER_KERNEL_NO	(20*32+30) /* CPU is not affected by SRSO across user/kernel boundaries */



/*

 * Extended auxiliary flags: Linux defined - for features scattered in various

arch/x86/kernel/cpu/bugs.c

+4 −0
Original line number Diff line number Diff line
@@ -2615,6 +2615,9 @@ static void __init srso_select_mitigation(void) 
		break;



	case SRSO_CMD_SAFE_RET:

		if (boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO))

			goto ibpb_on_vmexit;



		if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) {

			/*

			 * Enable the return thunk for generated code
@@ -2658,6 +2661,7 @@ static void __init srso_select_mitigation(void) 
		}

		break;



ibpb_on_vmexit:

	case SRSO_CMD_IBPB_ON_VMEXIT:

		if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) {

			if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {

arch/x86/kernel/cpu/common.c

+1 −0
Original line number Diff line number Diff line
@@ -1270,6 +1270,7 @@ static const struct x86_cpu_id cpu_vuln_blacklist[] __initconst = { 
	VULNBL_AMD(0x17, RETBLEED | SMT_RSB | SRSO),

	VULNBL_HYGON(0x18, RETBLEED | SMT_RSB | SRSO),

	VULNBL_AMD(0x19, SRSO),

	VULNBL_AMD(0x1a, SRSO),

	{}

};