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Subject[PATCH] x86-64: modify copy_user_generic() alternatives mechanism
In order to avoid unnecessary chains of branches, rather than
implementing copy_user_generic() as a function consisting of just a
single (possibly patched) branch, instead properly deal with patching
call instructions in the alternative instructions framework, and
move the patching into the callers.

As a follow-on, one could also introduce something like
__EXPORT_SYMBOL_ALT() to avoid patching call sites in modules.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: Nick Piggin <npiggin@suse.de>

---
arch/x86/include/asm/alternative.h | 7 ++++++-
arch/x86/include/asm/uaccess_64.h | 21 ++++++++++++++++++++-
arch/x86/kernel/alternative.c | 4 +++-
arch/x86/kernel/x8664_ksyms_64.c | 3 ++-
arch/x86/lib/copy_user_64.S | 6 ------
5 files changed, 31 insertions(+), 10 deletions(-)
--- linux-2.6.33-rc1/arch/x86/include/asm/alternative.h 2009-12-18 16:16:12.000000000 +0100
+++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/include/asm/alternative.h 2009-12-04 12:19:20.000000000 +0100
@@ -125,11 +125,16 @@ static inline void alternatives_smp_swit
asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
: output : "i" (0), ## input)

+/* Like alternative_io, but for replacing a direct call with another one. */
+#define alternative_call(oldfunc, newfunc, feature, output, input...) \
+ asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
+ : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
+
/*
* use this macro(s) if you need more than one output parameter
* in alternative_io
*/
-#define ASM_OUTPUT2(a, b) a, b
+#define ASM_OUTPUT2(a...) a

struct paravirt_patch_site;
#ifdef CONFIG_PARAVIRT
--- linux-2.6.33-rc1/arch/x86/include/asm/uaccess_64.h 2009-12-18 16:16:12.000000000 +0100
+++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/include/asm/uaccess_64.h 2009-12-04 12:19:20.000000000 +0100
@@ -8,6 +8,8 @@
#include <linux/errno.h>
#include <linux/prefetch.h>
#include <linux/lockdep.h>
+#include <asm/alternative.h>
+#include <asm/cpufeature.h>
#include <asm/page.h>

/*
@@ -16,7 +18,24 @@

/* Handles exceptions in both to and from, but doesn't do access_ok */
__must_check unsigned long
-copy_user_generic(void *to, const void *from, unsigned len);
+copy_user_generic_string(void *to, const void *from, unsigned len);
+__must_check unsigned long
+copy_user_generic_unrolled(void *to, const void *from, unsigned len);
+
+static __always_inline __must_check unsigned long
+copy_user_generic(void *to, const void *from, unsigned len)
+{
+ unsigned ret;
+
+ alternative_call(copy_user_generic_unrolled,
+ copy_user_generic_string,
+ X86_FEATURE_REP_GOOD,
+ ASM_OUTPUT2("=a" (ret), "=D" (to), "=S" (from),
+ "=d" (len)),
+ "1" (to), "2" (from), "3" (len)
+ : "memory", "rcx", "r8", "r9", "r10", "r11");
+ return ret;
+}

__must_check unsigned long
_copy_to_user(void __user *to, const void *from, unsigned len);
--- linux-2.6.33-rc1/arch/x86/kernel/alternative.c 2009-12-03 04:51:21.000000000 +0100
+++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/kernel/alternative.c 2009-12-04 12:19:20.000000000 +0100
@@ -205,7 +205,7 @@ void __init_or_module apply_alternatives
struct alt_instr *end)
{
struct alt_instr *a;
- char insnbuf[MAX_PATCH_LEN];
+ u8 insnbuf[MAX_PATCH_LEN];

DPRINTK("%s: alt table %p -> %p\n", __func__, start, end);
for (a = start; a < end; a++) {
@@ -223,6 +223,8 @@ void __init_or_module apply_alternatives
}
#endif
memcpy(insnbuf, a->replacement, a->replacementlen);
+ if (*insnbuf == 0xe8 && a->replacementlen == 5)
+ *(s32 *)(insnbuf + 1) += a->replacement - a->instr;
add_nops(insnbuf + a->replacementlen,
a->instrlen - a->replacementlen);
text_poke_early(instr, insnbuf, a->instrlen);
--- linux-2.6.33-rc1/arch/x86/kernel/x8664_ksyms_64.c 2009-12-18 16:16:13.000000000 +0100
+++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/kernel/x8664_ksyms_64.c 2009-12-04 12:19:20.000000000 +0100
@@ -26,7 +26,8 @@ EXPORT_SYMBOL(__put_user_2);
EXPORT_SYMBOL(__put_user_4);
EXPORT_SYMBOL(__put_user_8);

-EXPORT_SYMBOL(copy_user_generic);
+EXPORT_SYMBOL(copy_user_generic_string);
+EXPORT_SYMBOL(copy_user_generic_unrolled);
EXPORT_SYMBOL(__copy_user_nocache);
EXPORT_SYMBOL(_copy_from_user);
EXPORT_SYMBOL(_copy_to_user);
--- linux-2.6.33-rc1/arch/x86/lib/copy_user_64.S 2009-12-18 16:16:13.000000000 +0100
+++ 2.6.33-rc1-x86_64-copy_user_generic-alternative/arch/x86/lib/copy_user_64.S 2009-12-04 12:19:20.000000000 +0100
@@ -90,12 +90,6 @@ ENTRY(_copy_from_user)
CFI_ENDPROC
ENDPROC(_copy_from_user)

-ENTRY(copy_user_generic)
- CFI_STARTPROC
- ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string
- CFI_ENDPROC
-ENDPROC(copy_user_generic)
-
.section .fixup,"ax"
/* must zero dest */
ENTRY(bad_from_user)



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