[patch 06/11] Text Edit Lock - Alternative code for x86

Mathieu Desnoyers
2007-12-06T02:08:31Z

[-- Attachment #1: text-edit-lock-alternative-i386-and-x86_64.patch --]
[-- Type: text/plain, Size: 9688 bytes --]

Fix a memcpy that should be a text_poke (in apply_alternatives).

Use kernel_wp_save/kernel_wp_restore in text_poke to support DEBUG_RODATA
correctly and so the CPU HOTPLUG special case can be removed.

Add text_poke_early, for alternatives and paravirt boot-time and module load
time patching.

Notes:
- we use a macro for kernel_wp_save/restore to mimic local_irq_save/restore: the
argument is passed without &.

Changelog:

- Fix text_set and text_poke alignment check (mixed up bitwise and and or)
- Remove text_set
- Use the new macro INIT_ARRAY() to stop polluting the C files with ({ })
brackets (which breaks some c parsers in editors).
- Export add_nops, so it can be used by others.
- Remove x86 test for "wp_works_ok", it will just be ignored by the architecture
if not supported.
- Document text_poke_early.
- Remove clflush, since it breaks some VIA architectures and is not strictly
necessary.
- Add kerneldoc to text_poke and text_poke_early.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Andi Kleen <andi@firstfloor.org>
CC: pageexec@freemail.hu
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: H. Peter Anvin <hpa@zytor.com>
---
arch/x86/kernel/alternative.c | 58 ++++++++++++++++++++++++++++++++-------
include/asm-x86/alternative_32.h | 37 ++++++++++++++++++++++++
include/asm-x86/alternative_64.h | 39 +++++++++++++++++++++++++-
3 files changed, 122 insertions(+), 12 deletions(-)

Index: linux-2.6-lttng/arch/x86/kernel/alternative.c
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/alternative.c 2007-11-16 12:39:40.000000000 -0500
+++ linux-2.6-lttng/arch/x86/kernel/alternative.c 2007-11-16 12:42:50.000000000 -0500
@@ -173,7 +173,7 @@ static const unsigned char*const * find_
#endif /* CONFIG_X86_64 */

/* Use this to add nops to a buffer, then text_poke the whole buffer. */
-static void add_nops(void *insns, unsigned int len)
+void add_nops(void *insns, unsigned int len)
{
const unsigned char *const *noptable = find_nop_table();

@@ -186,6 +186,7 @@ static void add_nops(void *insns, unsign
len -= noplen;
}
}
+EXPORT_SYMBOL_GPL(add_nops);

extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
extern u8 *__smp_locks[], *__smp_locks_end[];
@@ -219,7 +220,7 @@ void apply_alternatives(struct alt_instr
memcpy(insnbuf, a->replacement, a->replacementlen);
add_nops(insnbuf + a->replacementlen,
a->instrlen - a->replacementlen);
- text_poke(instr, insnbuf, a->instrlen);
+ text_poke_early(instr, insnbuf, a->instrlen);
}
}

@@ -234,7 +235,8 @@ static void alternatives_smp_lock(u8 **s
continue;
if (*ptr > text_end)
continue;
- text_poke(*ptr, ((unsigned char []){0xf0}), 1); /* add lock prefix */
+ /* add lock prefix */
+ text_poke(*ptr, INIT_ARRAY(unsigned char, 0xf0, 1), 1);
};
}

@@ -397,7 +399,7 @@ void apply_paravirt(struct paravirt_patc

/* Pad the rest with nops */
add_nops(insnbuf + used, p->len - used);
- text_poke(p->instr, insnbuf, p->len);
+ text_poke_early(p->instr, insnbuf, p->len);
}
}
extern struct paravirt_patch_site __start_parainstructions[],
@@ -457,18 +459,54 @@ void __init alternative_instructions(voi
#endif
}

-/*
- * Warning:
+/**
+ * text_poke_early - Update instructions on a live kernel at boot time
+ * @addr: address to modify
+ * @opcode: source of the copy
+ * @len: length to copy
+ *
* When you use this code to patch more than one byte of an instruction
* you need to make sure that other CPUs cannot execute this code in parallel.
- * Also no thread must be currently preempted in the middle of these instructions.
- * And on the local CPU you need to be protected again NMI or MCE handlers
- * seeing an inconsistent instruction while you patch.
+ * Also no thread must be currently preempted in the middle of these
+ * instructions. And on the local CPU you need to be protected again NMI or MCE
+ * handlers seeing an inconsistent instruction while you patch.
+ * Warning: read_cr0 is modified by paravirt, this is why we have _early
+ * versions. They are not in the __init section because they can be used at
+ * module load time.
*/
-void __kprobes text_poke(void *addr, unsigned char *opcode, int len)
+void *text_poke_early(void *addr, const void *opcode, size_t len)
{
memcpy(addr, opcode, len);
sync_core();
/* Could also do a CLFLUSH here to speed up CPU recovery; but
that causes hangs on some VIA CPUs. */
+ return addr;
}
+
+/**
+ * text_poke - Update instructions on a live kernel
+ * @addr: address to modify
+ * @opcode: source of the copy
+ * @len: length to copy
+ *
+ * Only atomic text poke/set should be allowed when not doing early patching.
+ * It means the size must be writable atomically and the address must be aligned
+ * in a way that permits an atomic write.
+ */
+void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
+{
+ unsigned long cr0;
+
+ BUG_ON(len > sizeof(long));
+ BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1))
+ - ((long)addr & ~(sizeof(long) - 1)));
+ kernel_wp_save(cr0);
+ memcpy(addr, opcode, len);
+ kernel_wp_restore(cr0);
+ sync_core();
+ /* Could also do a CLFLUSH here to speed up CPU recovery; but
+ that causes hangs on some VIA CPUs. */
+ return addr;
+}
+
+
Index: linux-2.6-lttng/include/asm-x86/alternative_32.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-x86/alternative_32.h 2007-11-16 12:39:40.000000000 -0500
+++ linux-2.6-lttng/include/asm-x86/alternative_32.h 2007-11-16 12:40:03.000000000 -0500
@@ -4,6 +4,7 @@
#include <asm/types.h>
#include <linux/stddef.h>
#include <linux/types.h>
+#include <asm/processor-flags.h>

struct alt_instr {
u8 *instr; /* original instruction */
@@ -149,6 +150,40 @@ apply_paravirt(struct paravirt_patch_sit
#define __parainstructions_end NULL
#endif

-extern void text_poke(void *addr, unsigned char *opcode, int len);
+extern void add_nops(void *insns, unsigned int len);
+
+/*
+ * Clear and restore the kernel write-protection flag on the local CPU.
+ * Allows the kernel to edit read-only pages.
+ * Side-effect: any interrupt handler running between save and restore will have
+ * the ability to write to read-only pages.
+ *
+ * Warning:
+ * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
+ * no thread can be preempted in the instructions being modified (no iret to an
+ * invalid instruction possible) or if the instructions are changed from a
+ * consistent state to another consistent state atomically.
+ * More care must be taken when modifying code in the SMP case because of
+ * Intel's errata.
+ * On the local CPU you need to be protected again NMI or MCE handlers seeing an
+ * inconsistent instruction while you patch.
+ * The _early version does not use read_cr0(), which can be paravirtualized.
+ */
+
+extern void *text_poke(void *addr, const void *opcode, size_t len);
+extern void *text_poke_early(void *addr, const void *opcode, size_t len);
+
+#define kernel_wp_save(cr0) \
+ do { \
+ preempt_disable(); \
+ cr0 = read_cr0(); \
+ write_cr0(cr0 & ~X86_CR0_WP); \
+ } while (0)
+
+#define kernel_wp_restore(cr0) \
+ do { \
+ write_cr0(cr0); \
+ preempt_enable(); \
+ } while (0)

#endif /* _I386_ALTERNATIVE_H */
Index: linux-2.6-lttng/include/asm-x86/alternative_64.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-x86/alternative_64.h 2007-11-16 12:39:40.000000000 -0500
+++ linux-2.6-lttng/include/asm-x86/alternative_64.h 2007-11-16 12:40:03.000000000 -0500
@@ -5,6 +5,7 @@

#include <linux/types.h>
#include <linux/stddef.h>
+#include <asm/processor-flags.h>

/*
* Alternative inline assembly for SMP.
@@ -154,6 +155,42 @@ apply_paravirt(struct paravirt_patch *st
#define __parainstructions_end NULL
#endif

-extern void text_poke(void *addr, unsigned char *opcode, int len);
+extern void add_nops(void *insns, unsigned int len);
+
+/*
+ * Clear and restore the kernel write-protection flag on the local CPU.
+ * Allows the kernel to edit read-only pages.
+ * Side-effect: any interrupt handler running between save and restore will have
+ * the ability to write to read-only pages.
+ *
+ * Warning:
+ * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
+ * no thread can be preempted in the instructions being modified (no iret to an
+ * invalid instruction possible) or if the instructions are changed from a
+ * consistent state to another consistent state atomically.
+ * More care must be taken when modifying code in the SMP case because of
+ * Intel's errata.
+ * On the local CPU you need to be protected again NMI or MCE handlers seeing an
+ * inconsistent instruction while you patch.
+ * The _early version does not use read_cr0(), which can be paravirtualized.
+ */
+
+extern void *text_poke(void *addr, const void *opcode, size_t len);
+extern void *text_poke_early(void *addr, const void *opcode, size_t len);
+
+#define kernel_wp_save(cr0) \
+ do { \
+ typecheck(unsigned long, cr0); \
+ preempt_disable(); \
+ cr0 = read_cr0(); \
+ write_cr0(cr0 & ~X86_CR0_WP); \
+ } while (0)
+
+#define kernel_wp_restore(cr0) \
+ do { \
+ typecheck(unsigned long, cr0); \
+ write_cr0(cr0); \
+ preempt_enable(); \
+ } while (0)

#endif /* _X86_64_ALTERNATIVE_H */