[PATCH 9/9] powerpc/bpf: Emit stf barrier instruction sequences for BPF_NOSPEC

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

Emit similar instruction sequences to commit a048a07d7f4535
("powerpc/64s: Add support for a store forwarding barrier at kernel
entry/exit") when encountering BPF_NOSPEC.

Mitigations are enabled depending on what the firmware advertises. In
particular, we do not gate these mitigations based on current settings,
just like in x86. Due to this, we don't need to take any action if
mitigations are enabled or disabled at runtime.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
Thanks to Daniel Borkmann and Nick Piggin for their help in putting 
together this patch!


 arch/powerpc/net/bpf_jit64.h      |  8 ++---
 arch/powerpc/net/bpf_jit_comp64.c | 55 ++++++++++++++++++++++++++++---
 2 files changed, 55 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit64.h b/arch/powerpc/net/bpf_jit64.h
index 7b713edfa7e261..b63b35e45e558c 100644
--- a/arch/powerpc/net/bpf_jit64.h
+++ b/arch/powerpc/net/bpf_jit64.h
@@ -16,18 +16,18 @@
  * with our redzone usage.
  *
  *		[	prev sp		] <-------------
- *		[   nv gpr save area	] 6*8		|
+ *		[   nv gpr save area	] 5*8		|
  *		[    tail_call_cnt	] 8		|
- *		[    local_tmp_var	] 8		|
+ *		[    local_tmp_var	] 16		|
  * fp (r31) -->	[   ebpf stack space	] upto 512	|
  *		[     frame header	] 32/112	|
  * sp (r1) --->	[    stack pointer	] --------------
  */
 
 /* for gpr non volatile registers BPG_REG_6 to 10 */
-#define BPF_PPC_STACK_SAVE	(6*8)
+#define BPF_PPC_STACK_SAVE	(5*8)
 /* for bpf JIT code internal usage */
-#define BPF_PPC_STACK_LOCALS	16
+#define BPF_PPC_STACK_LOCALS	24
 /* stack frame excluding BPF stack, ensure this is quadword aligned */
 #define BPF_PPC_STACKFRAME	(STACK_FRAME_MIN_SIZE + \
 				 BPF_PPC_STACK_LOCALS + BPF_PPC_STACK_SAVE)
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 097d1ecfb9f562..df1666f0b54d9b 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -15,6 +15,7 @@
 #include <linux/if_vlan.h>
 #include <asm/kprobes.h>
 #include <linux/bpf.h>
+#include <asm/security_features.h>
 
 #include "bpf_jit64.h"
 
@@ -35,9 +36,9 @@ static inline bool bpf_has_stack_frame(struct codegen_context *ctx)
  *		[	prev sp		] <-------------
  *		[	  ...       	] 		|
  * sp (r1) --->	[    stack pointer	] --------------
- *		[   nv gpr save area	] 6*8
+ *		[   nv gpr save area	] 5*8
  *		[    tail_call_cnt	] 8
- *		[    local_tmp_var	] 8
+ *		[    local_tmp_var	] 16
  *		[   unused red zone	] 208 bytes protected
  */
 static int bpf_jit_stack_local(struct codegen_context *ctx)
@@ -45,12 +46,12 @@ static int bpf_jit_stack_local(struct codegen_context *ctx)
 	if (bpf_has_stack_frame(ctx))
 		return STACK_FRAME_MIN_SIZE + ctx->stack_size;
 	else
-		return -(BPF_PPC_STACK_SAVE + 16);
+		return -(BPF_PPC_STACK_SAVE + 24);
 }
 
 static int bpf_jit_stack_tailcallcnt(struct codegen_context *ctx)
 {
-	return bpf_jit_stack_local(ctx) + 8;
+	return bpf_jit_stack_local(ctx) + 16;
 }
 
 static int bpf_jit_stack_offsetof(struct codegen_context *ctx, int reg)
@@ -272,10 +273,33 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o
 	return 0;
 }
 
+/*
+ * We spill into the redzone always, even if the bpf program has its own stackframe.
+ * Offsets hardcoded based on BPF_PPC_STACK_SAVE -- see bpf_jit_stack_local()
+ */
+void bpf_stf_barrier(void);
+
+asm (
+"		.global bpf_stf_barrier		;"
+"	bpf_stf_barrier:			;"
+"		std	21,-64(1)		;"
+"		std	22,-56(1)		;"
+"		sync				;"
+"		ld	21,-64(1)		;"
+"		ld	22,-56(1)		;"
+"		ori	31,31,0			;"
+"		.rept 14			;"
+"		b	1f			;"
+"	1:					;"
+"		.endr				;"
+"		blr				;"
+);
+
 /* Assemble the body code between the prologue & epilogue */
 int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *ctx,
 		       u32 *addrs, bool extra_pass)
 {
+	enum stf_barrier_type stf_barrier = stf_barrier_type_get();
 	const struct bpf_insn *insn = fp->insnsi;
 	int flen = fp->len;
 	int i, ret;
@@ -643,6 +667,29 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
 		 * BPF_ST NOSPEC (speculation barrier)
 		 */
 		case BPF_ST | BPF_NOSPEC:
+			if (!security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) ||
+					!security_ftr_enabled(SEC_FTR_STF_BARRIER))
+				break;
+
+			switch (stf_barrier) {
+			case STF_BARRIER_EIEIO:
+				EMIT(PPC_RAW_EIEIO() | 0x02000000);
+				break;
+			case STF_BARRIER_SYNC_ORI:
+				EMIT(PPC_RAW_SYNC());
+				EMIT(PPC_RAW_LD(b2p[TMP_REG_1], _R13, 0));
+				EMIT(PPC_RAW_ORI(_R31, _R31, 0));
+				break;
+			case STF_BARRIER_FALLBACK:
+				EMIT(PPC_RAW_MFLR(b2p[TMP_REG_1]));
+				PPC_LI64(12, dereference_kernel_function_descriptor(bpf_stf_barrier));
+				EMIT(PPC_RAW_MTCTR(12));
+				EMIT(PPC_RAW_BCTRL());
+				EMIT(PPC_RAW_MTLR(b2p[TMP_REG_1]));
+				break;
+			case STF_BARRIER_NONE:
+				break;
+			}
 			break;
 
 		/*
-- 
2.33.0