powerpc/pseries: add new branch prediction security bits for link stack

The hypervisor interface has defined branch prediction security bits for
handling the link stack. Wire them up.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200825075612.224656-1-npiggin@gmail.com

arch/powerpc/include/asm/hvcall.h

@@ -375,11 +375,13 @@
 #define H_CPU_CHAR_THREAD_RECONFIG_CTRL	(1ull << 57) // IBM bit 6
 #define H_CPU_CHAR_COUNT_CACHE_DISABLED	(1ull << 56) // IBM bit 7
 #define H_CPU_CHAR_BCCTR_FLUSH_ASSIST	(1ull << 54) // IBM bit 9
+#define H_CPU_CHAR_BCCTR_LINK_FLUSH_ASSIST (1ull << 52) // IBM bit 11
 
 #define H_CPU_BEHAV_FAVOUR_SECURITY	(1ull << 63) // IBM bit 0
 #define H_CPU_BEHAV_L1D_FLUSH_PR	(1ull << 62) // IBM bit 1
 #define H_CPU_BEHAV_BNDS_CHK_SPEC_BAR	(1ull << 61) // IBM bit 2
 #define H_CPU_BEHAV_FLUSH_COUNT_CACHE	(1ull << 58) // IBM bit 5
+#define H_CPU_BEHAV_FLUSH_LINK_STACK	(1ull << 57) // IBM bit 6
 
 /* Flag values used in H_REGISTER_PROC_TBL hcall */
 #define PROC_TABLE_OP_MASK	0x18

arch/powerpc/platforms/pseries/setup.c

@@ -519,9 +519,15 @@ static void init_cpu_char_feature_flags(struct h_cpu_char_result *result)
 	if (result->character & H_CPU_CHAR_BCCTR_FLUSH_ASSIST)
 		security_ftr_set(SEC_FTR_BCCTR_FLUSH_ASSIST);
 
+	if (result->character & H_CPU_CHAR_BCCTR_LINK_FLUSH_ASSIST)
+		security_ftr_set(SEC_FTR_BCCTR_LINK_FLUSH_ASSIST);
+
 	if (result->behaviour & H_CPU_BEHAV_FLUSH_COUNT_CACHE)
 		security_ftr_set(SEC_FTR_FLUSH_COUNT_CACHE);
 
+	if (result->behaviour & H_CPU_BEHAV_FLUSH_LINK_STACK)
+		security_ftr_set(SEC_FTR_FLUSH_LINK_STACK);
+
 	/*
 	 * The features below are enabled by default, so we instead look to see
 	 * if firmware has *disabled* them, and clear them if so.