[PATCH stable v4.4 26/52] powerpc/64s: Add support for ori barrier_nospec patching

[Michael Ellerman]

From: Michal Suchanek <msuchanek at suse.de>

commit 2eea7f067f495e33b8b116b35b5988ab2b8aec55 upstream.

Based on the RFI patching. This is required to be able to disable the
speculation barrier.

Only one barrier type is supported and it does nothing when the
firmware does not enable it. Also re-patching modules is not supported
So the only meaningful thing that can be done is patching out the
speculation barrier at boot when the user says it is not wanted.

Signed-off-by: Michal Suchanek <msuchanek at suse.de>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
---
 arch/powerpc/include/asm/barrier.h        |  2 +-
 arch/powerpc/include/asm/feature-fixups.h |  9 ++++++++
 arch/powerpc/include/asm/setup.h          |  1 +
 arch/powerpc/kernel/security.c            |  9 ++++++++
 arch/powerpc/kernel/vmlinux.lds.S         |  7 ++++++
 arch/powerpc/lib/feature-fixups.c         | 27 +++++++++++++++++++++++
 6 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
index ef86063c662a..8e7cbf0ea614 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -97,7 +97,7 @@ do {									\
  * Prevent execution of subsequent instructions until preceding branches have
  * been fully resolved and are no longer executing speculatively.
  */
-#define barrier_nospec_asm ori 31,31,0
+#define barrier_nospec_asm NOSPEC_BARRIER_FIXUP_SECTION; nop
 
 // This also acts as a compiler barrier due to the memory clobber.
 #define barrier_nospec() asm (stringify_in_c(barrier_nospec_asm) ::: "memory")
diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h
index 350be873a941..7983390ff0a9 100644
--- a/arch/powerpc/include/asm/feature-fixups.h
+++ b/arch/powerpc/include/asm/feature-fixups.h
@@ -208,6 +208,14 @@ label##3:					       	\
 	FTR_ENTRY_OFFSET 951b-952b;			\
 	.popsection;
 
+#define NOSPEC_BARRIER_FIXUP_SECTION			\
+953:							\
+	.pushsection __barrier_nospec_fixup,"a";	\
+	.align 2;					\
+954:							\
+	FTR_ENTRY_OFFSET 953b-954b;			\
+	.popsection;
+
 
 #ifndef __ASSEMBLY__
 
@@ -215,6 +223,7 @@ extern long stf_barrier_fallback;
 extern long __start___stf_entry_barrier_fixup, __stop___stf_entry_barrier_fixup;
 extern long __start___stf_exit_barrier_fixup, __stop___stf_exit_barrier_fixup;
 extern long __start___rfi_flush_fixup, __stop___rfi_flush_fixup;
+extern long __start___barrier_nospec_fixup, __stop___barrier_nospec_fixup;
 
 #endif
 
diff --git a/arch/powerpc/include/asm/setup.h b/arch/powerpc/include/asm/setup.h
index 3733195be997..80c35275bbdb 100644
--- a/arch/powerpc/include/asm/setup.h
+++ b/arch/powerpc/include/asm/setup.h
@@ -38,6 +38,7 @@ enum l1d_flush_type {
 
 void setup_rfi_flush(enum l1d_flush_type, bool enable);
 void do_rfi_flush_fixups(enum l1d_flush_type types);
+void do_barrier_nospec_fixups(bool enable);
 
 #endif /* !__ASSEMBLY__ */
 
diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index e19216472ed7..0b7f6471f8f5 100644
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c
@@ -11,10 +11,19 @@
 
 #include <asm/debug.h>
 #include <asm/security_features.h>
+#include <asm/setup.h>
 
 
 unsigned long powerpc_security_features __read_mostly = SEC_FTR_DEFAULT;
 
+static bool barrier_nospec_enabled;
+
+static void enable_barrier_nospec(bool enable)
+{
+	barrier_nospec_enabled = enable;
+	do_barrier_nospec_fixups(enable);
+}
+
 ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf)
 {
 	bool thread_priv;
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index b454e27d784d..977e859b4d4c 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -93,6 +93,13 @@ SECTIONS
 		*(__rfi_flush_fixup)
 		__stop___rfi_flush_fixup = .;
 	}
+
+	. = ALIGN(8);
+	__spec_barrier_fixup : AT(ADDR(__spec_barrier_fixup) - LOAD_OFFSET) {
+		__start___barrier_nospec_fixup = .;
+		*(__barrier_nospec_fixup)
+		__stop___barrier_nospec_fixup = .;
+	}
 #endif
 
 	EXCEPTION_TABLE(0)
diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index a1865309b7fc..17a3c2d5c80b 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -274,6 +274,33 @@ void do_rfi_flush_fixups(enum l1d_flush_type types)
 		(types &  L1D_FLUSH_MTTRIG)     ? "mttrig type"
 						: "unknown");
 }
+
+void do_barrier_nospec_fixups(bool enable)
+{
+	unsigned int instr, *dest;
+	long *start, *end;
+	int i;
+
+	start = PTRRELOC(&__start___barrier_nospec_fixup),
+	end = PTRRELOC(&__stop___barrier_nospec_fixup);
+
+	instr = 0x60000000; /* nop */
+
+	if (enable) {
+		pr_info("barrier-nospec: using ORI speculation barrier\n");
+		instr = 0x63ff0000; /* ori 31,31,0 speculation barrier */
+	}
+
+	for (i = 0; start < end; start++, i++) {
+		dest = (void *)start + *start;
+
+		pr_devel("patching dest %lx\n", (unsigned long)dest);
+		patch_instruction(dest, instr);
+	}
+
+	printk(KERN_DEBUG "barrier-nospec: patched %d locations\n", i);
+}
+
 #endif /* CONFIG_PPC_BOOK3S_64 */
 
 void do_lwsync_fixups(unsigned long value, void *fixup_start, void *fixup_end)
-- 
2.20.1