linux-kernel - [RFC v5 11/57] objtool: Abstract alternative special case handling

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Date:   Thu,  9 Jan 2020 16:02:14 +0000
From:   Julien Thierry <jthierry@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     jpoimboe@...hat.com, peterz@...radead.org, raphael.gault@....com,
        catalin.marinas@....com, will@...nel.org,
        Julien Thierry <jthierry@...hat.com>
Subject: [RFC v5 11/57] objtool: Abstract alternative special case handling

Some alternatives associated with a specific feature need to be treated
in a special way. Since the features and how to treat them vary from one
architecture to another, move the special case handling to arch specific
code.

Signed-off-by: Julien Thierry <jthierry@...hat.com>
---
 tools/objtool/arch/x86/Build                  |  1 +
 tools/objtool/arch/x86/arch_special.c         | 34 +++++++++++++++++++
 tools/objtool/arch/x86/include/arch_special.h |  5 +++
 tools/objtool/special.c                       | 25 +-------------
 tools/objtool/special.h                       |  8 +++++
 5 files changed, 49 insertions(+), 24 deletions(-)
 create mode 100644 tools/objtool/arch/x86/arch_special.c

diff --git a/tools/objtool/arch/x86/Build b/tools/objtool/arch/x86/Build
index e43fd6fa0ee1..971f9fa90a3c 100644
--- a/tools/objtool/arch/x86/Build
+++ b/tools/objtool/arch/x86/Build
@@ -1,3 +1,4 @@
+objtool-y += arch_special.o
 objtool-y += decode.o
 objtool-y += orc_dump.o
 objtool-y += orc_gen.o
diff --git a/tools/objtool/arch/x86/arch_special.c b/tools/objtool/arch/x86/arch_special.c
new file mode 100644
index 000000000000..6dba31f419d0
--- /dev/null
+++ b/tools/objtool/arch/x86/arch_special.c
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include "../../special.h"
+#include "../../builtin.h"
+
+void arch_handle_alternative(unsigned short feature, struct special_alt *alt)
+{
+	/*
+	 * If UACCESS validation is enabled; force that alternative;
+	 * otherwise force it the other way.
+	 *
+	 * What we want to avoid is having both the original and the
+	 * alternative code flow at the same time, in that case we can
+	 * find paths that see the STAC but take the NOP instead of
+	 * CLAC and the other way around.
+	 */
+	switch (feature) {
+	case X86_FEATURE_SMAP:
+		if (uaccess)
+			alt->skip_orig = true;
+		else
+			alt->skip_alt = true;
+		break;
+	case X86_FEATURE_POPCNT:
+		/*
+		 * It has been requested that we don't validate the !POPCNT
+		 * feature path which is a "very very small percentage of
+		 * machines".
+		 */
+		alt->skip_orig = true;
+		break;
+	default:
+		break;
+	}
+}
diff --git a/tools/objtool/arch/x86/include/arch_special.h b/tools/objtool/arch/x86/include/arch_special.h
index 426178d504a8..3ab2dc32424b 100644
--- a/tools/objtool/arch/x86/include/arch_special.h
+++ b/tools/objtool/arch/x86/include/arch_special.h
@@ -20,4 +20,9 @@
 #define X86_FEATURE_POPCNT (4 * 32 + 23)
 #define X86_FEATURE_SMAP   (9 * 32 + 20)
 
+struct special_alt;
+
+#define arch_handle_alternative arch_handle_alternative
+void arch_handle_alternative(unsigned short feature, struct special_alt *alt);
+
 #endif /* _X86_ARCH_SPECIAL_H */
diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index b8ccee1b5382..67461b25e649 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -75,30 +75,7 @@ static int get_alt_entry(struct elf *elf, struct special_entry *entry,
 
 		feature = *(unsigned short *)(sec->data->d_buf + offset +
 					      entry->feature);
-
-		/*
-		 * It has been requested that we don't validate the !POPCNT
-		 * feature path which is a "very very small percentage of
-		 * machines".
-		 */
-		if (feature == X86_FEATURE_POPCNT)
-			alt->skip_orig = true;
-
-		/*
-		 * If UACCESS validation is enabled; force that alternative;
-		 * otherwise force it the other way.
-		 *
-		 * What we want to avoid is having both the original and the
-		 * alternative code flow at the same time, in that case we can
-		 * find paths that see the STAC but take the NOP instead of
-		 * CLAC and the other way around.
-		 */
-		if (feature == X86_FEATURE_SMAP) {
-			if (uaccess)
-				alt->skip_orig = true;
-			else
-				alt->skip_alt = true;
-		}
+		arch_handle_alternative(feature, alt);
 	}
 
 	orig_rela = find_rela_by_dest(sec, offset + entry->orig);
diff --git a/tools/objtool/special.h b/tools/objtool/special.h
index 35061530e46e..738a05bc6d3a 100644
--- a/tools/objtool/special.h
+++ b/tools/objtool/special.h
@@ -8,6 +8,7 @@
 
 #include <stdbool.h>
 #include "elf.h"
+#include "arch_special.h"
 
 struct special_alt {
 	struct list_head list;
@@ -28,4 +29,11 @@ struct special_alt {
 
 int special_get_alts(struct elf *elf, struct list_head *alts);
 
+#ifndef arch_handle_alternative
+static inline void arch_handle_alternative(unsigned short feature,
+					   struct special_alt *alt)
+{
+}
+#endif
+
 #endif /* _SPECIAL_H */
-- 
2.21.0