[PATCH] Fix zeroing on exception in copy_*_user

- Don't zero for __copy_from_user_inatomic following i386.
This will prevent spurious zeros for parallel file system writers when
one does a exception
- The string instruction version didn't zero the output on
exception. Oops.

Also I cleaned up the code a bit while I was at it and added a minor
optimization to the string instruction path.

Signed-off-by: Andi Kleen <ak@suse.de>

2 files changed, 80 insertions, 45 deletions

diff --git a/arch/x86_64/kernel/x8664_ksyms.c b/arch/x86_64/kernel/x8664_ksyms.c
index 370952c4ff22..c3454af5e3a2 100644
--- a/arch/x86_64/kernel/x8664_ksyms.c
+++ b/arch/x86_64/kernel/x8664_ksyms.c
@@ -29,6 +29,7 @@ EXPORT_SYMBOL(__put_user_8);
 EXPORT_SYMBOL(copy_user_generic);
 EXPORT_SYMBOL(copy_from_user);
 EXPORT_SYMBOL(copy_to_user);
+EXPORT_SYMBOL(__copy_from_user_inatomic);
 
 EXPORT_SYMBOL(copy_page);
 EXPORT_SYMBOL(clear_page);
diff --git a/arch/x86_64/lib/copy_user.S b/arch/x86_64/lib/copy_user.S
index 962f3a693c5e..70bebd310408 100644
--- a/arch/x86_64/lib/copy_user.S
+++ b/arch/x86_64/lib/copy_user.S
@@ -9,10 +9,29 @@
 
 #define FIX_ALIGNMENT 1
 
-        #include <asm/current.h>
-        #include <asm/asm-offsets.h>
-        #include <asm/thread_info.h>
-        #include <asm/cpufeature.h>
+#include <asm/current.h>
+#include <asm/asm-offsets.h>
+#include <asm/thread_info.h>
+#include <asm/cpufeature.h>
+
+        .macro ALTERNATIVE_JUMP feature,orig,alt
+0:
+        .byte 0xe9      /* 32bit jump */
+        .long \orig-1f  /* by default jump to orig */
+1:
+        .section .altinstr_replacement,"ax"
+2:      .byte 0xe9                   /* near jump with 32bit immediate */
+        .long \alt-1b /* offset */   /* or alternatively to alt */
+        .previous
+        .section .altinstructions,"a"
+        .align 8
+        .quad  0b
+        .quad  2b
+        .byte  \feature              /* when feature is set */
+        .byte  5
+        .byte  5
+        .previous
+        .endm
 
 /* Standard copy_to_user with segment limit checking */         
 ENTRY(copy_to_user)
@@ -23,25 +42,21 @@ ENTRY(copy_to_user)
         jc  bad_to_user
         cmpq threadinfo_addr_limit(%rax),%rcx
         jae bad_to_user
-2:
-        .byte 0xe9      /* 32bit jump */
-        .long .Lcug-1f
-1:
+        xorl %eax,%eax  /* clear zero flag */
+        ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string
         CFI_ENDPROC
-ENDPROC(copy_to_user)
 
-        .section .altinstr_replacement,"ax"
-3:      .byte 0xe9                      /* replacement jmp with 32 bit immediate */
-        .long copy_user_generic_c-1b    /* offset */
-        .previous
-        .section .altinstructions,"a"
-        .align 8
-        .quad  2b
-        .quad  3b
-        .byte  X86_FEATURE_REP_GOOD
-        .byte  5
-        .byte  5
-        .previous
+ENTRY(copy_user_generic)
+        CFI_STARTPROC
+        movl $1,%ecx    /* set zero flag */
+        ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string
+        CFI_ENDPROC
+
+ENTRY(__copy_from_user_inatomic)
+        CFI_STARTPROC
+        xorl %ecx,%ecx  /* clear zero flag */
+        ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string
+        CFI_ENDPROC
 
 /* Standard copy_from_user with segment limit checking */       
 ENTRY(copy_from_user)
@@ -52,7 +67,8 @@ ENTRY(copy_from_user)
         jc  bad_from_user
         cmpq threadinfo_addr_limit(%rax),%rcx
         jae  bad_from_user
-        /* FALL THROUGH to copy_user_generic */
+        movl $1,%ecx    /* set zero flag */
+        ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string
         CFI_ENDPROC
 ENDPROC(copy_from_user)
         
@@ -73,37 +89,26 @@ END(bad_from_user)
         
                 
 /*
- * copy_user_generic - memory copy with exception handling.
+ * copy_user_generic_unrolled - memory copy with exception handling.
+ * This version is for CPUs like P4 that don't have efficient micro code for rep movsq
  *      
  * Input:       
  * rdi destination
  * rsi source
  * rdx count
+ * ecx zero flag -- if true zero destination on error
  *
  * Output:              
  * eax uncopied bytes or 0 if successful.
  */
-ENTRY(copy_user_generic)
+ENTRY(copy_user_generic_unrolled)
         CFI_STARTPROC
-        .byte 0x66,0x66,0x90    /* 5 byte nop for replacement jump */
-        .byte 0x66,0x90
-1:
-        .section .altinstr_replacement,"ax"
-2:      .byte 0xe9                   /* near jump with 32bit immediate */
-        .long copy_user_generic_c-1b /* offset */
-        .previous
-        .section .altinstructions,"a"
-        .align 8
-        .quad  copy_user_generic
-        .quad  2b
-        .byte  X86_FEATURE_REP_GOOD
-        .byte  5
-        .byte  5
-        .previous
-.Lcug:
         pushq %rbx
         CFI_ADJUST_CFA_OFFSET 8
         CFI_REL_OFFSET rbx, 0
+        pushq %rcx
+        CFI_ADJUST_CFA_OFFSET 8
+        CFI_REL_OFFSET rcx, 0
         xorl %eax,%eax          /*zero for the exception handler */
 
 #ifdef FIX_ALIGNMENT
@@ -179,6 +184,9 @@ ENTRY(copy_user_generic)
 
         CFI_REMEMBER_STATE
 .Lende:
+        popq %rcx
+        CFI_ADJUST_CFA_OFFSET -8
+        CFI_RESTORE rcx
         popq %rbx
         CFI_ADJUST_CFA_OFFSET -8
         CFI_RESTORE rbx
@@ -265,6 +273,8 @@ ENTRY(copy_user_generic)
         addl %ecx,%edx
         /* edx: bytes to zero, rdi: dest, eax:zero */
 .Lzero_rest:
+        cmpl $0,(%rsp)
+        jz   .Le_zero
         movq %rdx,%rcx
 .Le_byte:
         xorl %eax,%eax
@@ -286,6 +296,7 @@ ENDPROC(copy_user_generic)
  /* rdi destination
   * rsi source
   * rdx count
+  * ecx zero flag
   *
   * Output:
   * eax uncopied bytes or 0 if successfull.
@@ -296,25 +307,48 @@ ENDPROC(copy_user_generic)
   * And more would be dangerous because both Intel and AMD have
   * errata with rep movsq > 4GB. If someone feels the need to fix
   * this please consider this.
-   */
-copy_user_generic_c:
+  */
+ENTRY(copy_user_generic_string)
         CFI_STARTPROC
+        movl %ecx,%r8d          /* save zero flag */
         movl %edx,%ecx
         shrl $3,%ecx
         andl $7,%edx    
+        jz   10f
 1:      rep 
         movsq 
         movl %edx,%ecx
 2:      rep
         movsb
-4:      movl %ecx,%eax
+9:      movl %ecx,%eax
         ret
-3:      lea (%rdx,%rcx,8),%rax
+
+        /* multiple of 8 byte */
+10:     rep
+        movsq
+        xor %eax,%eax
         ret
+
+        /* exception handling */
+3:      lea (%rdx,%rcx,8),%rax  /* exception on quad loop */
+        jmp 6f
+5:      movl %ecx,%eax          /* exception on byte loop */
+        /* eax: left over bytes */
+6:      testl %r8d,%r8d         /* zero flag set? */
+        jz 7f
+        movl %eax,%ecx          /* initialize x86 loop counter */
+        push %rax
+        xorl %eax,%eax
+8:      rep
+        stosb                   /* zero the rest */
+11:     pop %rax
+7:      ret
         CFI_ENDPROC
 END(copy_user_generic_c)
 
         .section __ex_table,"a"
         .quad 1b,3b
-        .quad 2b,4b
+        .quad 2b,5b
+        .quad 8b,11b
+        .quad 10b,3b
         .previous