linux-kernel - [PATCH 3/5] MIPS: Add support for 64-bit R6 ELF relocations

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Date:	Wed, 3 Feb 2016 03:44:43 +0000
From:	Paul Burton <paul.burton@...tec.com>
To:	<linux-mips@...ux-mips.org>, Ralf Baechle <ralf@...ux-mips.org>
CC:	"Steven J. Hill" <Steven.Hill@...tec.com>,
	James Hogan <james.hogan@...tec.com>,
	Paul Burton <paul.burton@...tec.com>,
	"Maciej W. Rozycki" <macro@...tec.com>,
	Kees Cook <keescook@...omium.org>,
	<linux-kernel@...r.kernel.org>,
	Markos Chandras <markos.chandras@...tec.com>,
	Alex Smith <alex.smith@...tec.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 3/5] MIPS: Add support for 64-bit R6 ELF relocations

From: "Steven J. Hill" <Steven.Hill@...tec.com>

This patch fixes MIPS64r6 kernel modules by adding new ELF
relocations. Toolchains that compile 64-bit R6 binaries emit
two new ELF relocations R_MIPS_PC21_S2 and R_MIPS_PC26_S2.
The pre-existing R_MIPS_PC16 ELF relocation is also emitted.

Signed-off-by: Steven J. Hill <Steven.Hill@...tec.com>
Signed-off-by: James Hogan <james.hogan@...tec.com>
Signed-off-by: Paul Burton <paul.burton@...tec.com>
---

 arch/mips/include/asm/elf.h    |  5 +++
 arch/mips/kernel/module-rela.c | 69 +++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/elf.h b/arch/mips/include/asm/elf.h
index cefb7a5..7cec234 100644
--- a/arch/mips/include/asm/elf.h
+++ b/arch/mips/include/asm/elf.h
@@ -111,6 +111,11 @@
 #define R_MIPS_CALLHI16		30
 #define R_MIPS_CALLLO16		31
 /*
+ * Introduced for MIPSr6.
+ */
+#define R_MIPS_PC21_S2		60
+#define R_MIPS_PC26_S2		61
+/*
  * This range is reserved for vendor specific relocations.
  */
 #define R_MIPS_LOVENDOR		100
diff --git a/arch/mips/kernel/module-rela.c b/arch/mips/kernel/module-rela.c
index f1ff64b..2dbe1b0 100644
--- a/arch/mips/kernel/module-rela.c
+++ b/arch/mips/kernel/module-rela.c
@@ -16,6 +16,7 @@
  *  Copyright (C) 2001 Rusty Russell.
  *  Copyright (C) 2003, 2004 Ralf Baechle (ralf@...ux-mips.org)
  *  Copyright (C) 2005 Thiemo Seufer
+ *  Copyright (C) 2015 Imagination Technologies Ltd.
  */
 
 #include <linux/elf.h>
@@ -65,6 +66,27 @@ static int apply_r_mips_lo16_rela(struct module *me, u32 *location, Elf_Addr v)
 	return 0;
 }
 
+static int apply_r_mips_pc16_rela(struct module *me, u32 *location, Elf_Addr v)
+{
+	long offset;
+
+	if (v % 4) {
+		pr_err("module %s: dangerous R_MIPS_PC16 RELA relocation\n",
+		       me->name);
+		return -ENOEXEC;
+	}
+
+	offset = ((long)v - (long)location) >> 2;
+	if (offset != (int16_t)offset) {
+		pr_err("module %s: relocation overflow\n", me->name);
+		return -ENOEXEC;
+	}
+
+	*location = (*location & ~0xffff) | (offset & 0xffff);
+
+	return 0;
+}
+
 static int apply_r_mips_64_rela(struct module *me, u32 *location, Elf_Addr v)
 {
 	*(Elf_Addr *)location = v;
@@ -90,6 +112,48 @@ static int apply_r_mips_highest_rela(struct module *me, u32 *location,
 	return 0;
 }
 
+static int apply_r_mips_pc21_rela(struct module *me, u32 *location, Elf_Addr v)
+{
+	long offset;
+
+	if (v % 4) {
+		pr_err("module %s: dangerous R_MIPS_PC21 RELA relocation\n",
+		       me->name);
+		return -ENOEXEC;
+	}
+
+	offset = ((long)v - (long)location) >> 2;
+	if ((offset >> 20) > 0 || (offset >> 20) < -1) {
+		pr_err("module %s: relocation overflow\n", me->name);
+		return -ENOEXEC;
+	}
+
+	*location = (*location & ~0x001fffff) | (offset & 0x001fffff);
+
+	return 0;
+}
+
+static int apply_r_mips_pc26_rela(struct module *me, u32 *location, Elf_Addr v)
+{
+	long offset;
+
+	if (v % 4) {
+		pr_err("module %s: dangerous R_MIPS_PC26 RELA relocation\n",
+		       me->name);
+		return -ENOEXEC;
+	}
+
+	offset = ((long)v - (long)location) >> 2;
+	if ((offset >> 25) > 0 || (offset >> 25) < -1) {
+		pr_err("module %s: relocation overflow\n", me->name);
+		return -ENOEXEC;
+	}
+
+	*location = (*location & ~0x03ffffff) | (offset & 0x03ffffff);
+
+	return 0;
+}
+
 static int (*reloc_handlers_rela[]) (struct module *me, u32 *location,
 				Elf_Addr v) = {
 	[R_MIPS_NONE]		= apply_r_mips_none,
@@ -97,9 +161,12 @@ static int (*reloc_handlers_rela[]) (struct module *me, u32 *location,
 	[R_MIPS_26]		= apply_r_mips_26_rela,
 	[R_MIPS_HI16]		= apply_r_mips_hi16_rela,
 	[R_MIPS_LO16]		= apply_r_mips_lo16_rela,
+	[R_MIPS_PC16]		= apply_r_mips_pc16_rela,
 	[R_MIPS_64]		= apply_r_mips_64_rela,
 	[R_MIPS_HIGHER]		= apply_r_mips_higher_rela,
-	[R_MIPS_HIGHEST]	= apply_r_mips_highest_rela
+	[R_MIPS_HIGHEST]	= apply_r_mips_highest_rela,
+	[R_MIPS_PC21_S2]	= apply_r_mips_pc21_rela,
+	[R_MIPS_PC26_S2]	= apply_r_mips_pc26_rela,
 };
 
 int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
-- 
2.7.0