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 <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Andrew Morton <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 69b74a7..3b5b828 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -125,11 +125,16 @@
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
diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
index 46324c6..a78c403 100644
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -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);
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index de7353c..2589ea4 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -205,7 +205,7 @@
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 @@
}
#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);
diff --git a/arch/x86/kernel/x8664_ksyms_64.c b/arch/x86/kernel/x8664_ksyms_64.c
index 619f7f8..693920b 100644
--- a/arch/x86/kernel/x8664_ksyms_64.c
+++ b/arch/x86/kernel/x8664_ksyms_64.c
@@ -26,7 +26,8 @@
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);
diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index cf889d4..71100c9 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -90,12 +90,6 @@
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)
