[PATCH stable v4.4 45/52] powerpc/fsl: Add infrastructure to fixup branch predictor flush

[Michael Ellerman]

From: Diana Craciun <diana.craciun at nxp.com>

commit 76a5eaa38b15dda92cd6964248c39b5a6f3a4e9d upstream.

In order to protect against speculation attacks (Spectre
variant 2) on NXP PowerPC platforms, the branch predictor
should be flushed when the privillege level is changed.
This patch is adding the infrastructure to fixup at runtime
the code sections that are performing the branch predictor flush
depending on a boot arg parameter which is added later in a
separate patch.

Signed-off-by: Diana Craciun <diana.craciun at nxp.com>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
---
 arch/powerpc/include/asm/feature-fixups.h | 12 ++++++++++++
 arch/powerpc/include/asm/setup.h          |  2 ++
 arch/powerpc/kernel/vmlinux.lds.S         |  8 ++++++++
 arch/powerpc/lib/feature-fixups.c         | 23 +++++++++++++++++++++++
 4 files changed, 45 insertions(+)

diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h
index 7983390ff0a9..145a37ab2d3e 100644
--- a/arch/powerpc/include/asm/feature-fixups.h
+++ b/arch/powerpc/include/asm/feature-fixups.h
@@ -216,6 +216,17 @@ label##3:					       	\
 	FTR_ENTRY_OFFSET 953b-954b;			\
 	.popsection;
 
+#define START_BTB_FLUSH_SECTION			\
+955:							\
+
+#define END_BTB_FLUSH_SECTION			\
+956:							\
+	.pushsection __btb_flush_fixup,"a";	\
+	.align 2;							\
+957:						\
+	FTR_ENTRY_OFFSET 955b-957b;			\
+	FTR_ENTRY_OFFSET 956b-957b;			\
+	.popsection;
 
 #ifndef __ASSEMBLY__
 
@@ -224,6 +235,7 @@ 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;
+extern long __start__btb_flush_fixup, __stop__btb_flush_fixup;
 
 #endif
 
diff --git a/arch/powerpc/include/asm/setup.h b/arch/powerpc/include/asm/setup.h
index 21daee862399..4d6446408a1b 100644
--- a/arch/powerpc/include/asm/setup.h
+++ b/arch/powerpc/include/asm/setup.h
@@ -53,6 +53,8 @@ void do_barrier_nospec_fixups_range(bool enable, void *start, void *end);
 static inline void do_barrier_nospec_fixups_range(bool enable, void *start, void *end) { };
 #endif
 
+void do_btb_flush_fixups(void);
+
 #endif /* !__ASSEMBLY__ */
 
 #endif	/* _ASM_POWERPC_SETUP_H */
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 4f9e7733e015..876ac9d52afc 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -104,6 +104,14 @@ SECTIONS
 	}
 #endif /* CONFIG_PPC_BARRIER_NOSPEC */
 
+#ifdef CONFIG_PPC_FSL_BOOK3E
+	. = ALIGN(8);
+	__spec_btb_flush_fixup : AT(ADDR(__spec_btb_flush_fixup) - LOAD_OFFSET) {
+		__start__btb_flush_fixup = .;
+		*(__btb_flush_fixup)
+		__stop__btb_flush_fixup = .;
+	}
+#endif
 	EXCEPTION_TABLE(0)
 
 	NOTES :kernel :notes
diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
index 68e089a48b2f..7bdfc19a491d 100644
--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c
@@ -344,6 +344,29 @@ void do_barrier_nospec_fixups_range(bool enable, void *fixup_start, void *fixup_
 
 	printk(KERN_DEBUG "barrier-nospec: patched %d locations\n", i);
 }
+
+static void patch_btb_flush_section(long *curr)
+{
+	unsigned int *start, *end;
+
+	start = (void *)curr + *curr;
+	end = (void *)curr + *(curr + 1);
+	for (; start < end; start++) {
+		pr_devel("patching dest %lx\n", (unsigned long)start);
+		patch_instruction(start, PPC_INST_NOP);
+	}
+}
+
+void do_btb_flush_fixups(void)
+{
+	long *start, *end;
+
+	start = PTRRELOC(&__start__btb_flush_fixup);
+	end = PTRRELOC(&__stop__btb_flush_fixup);
+
+	for (; start < end; start += 2)
+		patch_btb_flush_section(start);
+}
 #endif /* CONFIG_PPC_FSL_BOOK3E */
 
 void do_lwsync_fixups(unsigned long value, void *fixup_start, void *fixup_end)
-- 
2.20.1