x86/speculation: Fix firmware entry SPEC_CTRL handling

The firmware entry code may accidentally clear STIBP or SSBD. Fix that.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>

arch/x86/include/asm/nospec-branch.h

@@ -285,18 +285,16 @@ extern u64 spec_ctrl_current(void);
  */
 #define firmware_restrict_branch_speculation_start()			\
 do {									\
-	u64 val = x86_spec_ctrl_base | SPEC_CTRL_IBRS;			\
-									\
 	preempt_disable();						\
-	alternative_msr_write(MSR_IA32_SPEC_CTRL, val,			\
+	alternative_msr_write(MSR_IA32_SPEC_CTRL,			\
+			      spec_ctrl_current() | SPEC_CTRL_IBRS,	\
 			      X86_FEATURE_USE_IBRS_FW);			\
 } while (0)
 
 #define firmware_restrict_branch_speculation_end()			\
 do {									\
-	u64 val = x86_spec_ctrl_base;					\
-									\
-	alternative_msr_write(MSR_IA32_SPEC_CTRL, val,			\
+	alternative_msr_write(MSR_IA32_SPEC_CTRL,			\
+			      spec_ctrl_current(),			\
 			      X86_FEATURE_USE_IBRS_FW);			\
 	preempt_enable();						\
 } while (0)