patches/kernel/0075-x86-entry-Use-SYSCALL_DEFINE-macros-for-sys_modify_l.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Dave Hansen <dave.hansen@linux.intel.com>
   3 Date: Wed, 18 Oct 2017 10:21:07 -0700
   4 Subject: [PATCH] x86/entry: Use SYSCALL_DEFINE() macros for sys_modify_ldt()
   5 MIME-Version: 1.0
   6 Content-Type: text/plain; charset=UTF-8
   7 Content-Transfer-Encoding: 8bit
   8
   9 CVE-2017-5754
  10
  11 We do not have tracepoints for sys_modify_ldt() because we define
  12 it directly instead of using the normal SYSCALL_DEFINEx() macros.
  13
  14 However, there is a reason sys_modify_ldt() does not use the macros:
  15 it has an 'int' return type instead of 'unsigned long'.  This is
  16 a bug, but it's a bug cemented in the ABI.
  17
  18 What does this mean?  If we return -EINVAL from a function that
  19 returns 'int', we have 0x00000000ffffffea in %rax.  But, if we
  20 return -EINVAL from a function returning 'unsigned long', we end
  21 up with 0xffffffffffffffea in %rax, which is wrong.
  22
  23 To work around this and maintain the 'int' behavior while using
  24 the SYSCALL_DEFINEx() macros, so we add a cast to 'unsigned int'
  25 in both implementations of sys_modify_ldt().
  26
  27 Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
  28 Reviewed-by: Andy Lutomirski <luto@kernel.org>
  29 Reviewed-by: Brian Gerst <brgerst@gmail.com>
  30 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  31 Cc: Peter Zijlstra <peterz@infradead.org>
  32 Cc: Thomas Gleixner <tglx@linutronix.de>
  33 Link: http://lkml.kernel.org/r/20171018172107.1A79C532@viggo.jf.intel.com
  34 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  35 (cherry picked from commit da20ab35180780e4a6eadc804544f1fa967f3567)
  36 Signed-off-by: Andy Whitcroft <apw@canonical.com>
  37 Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
  38 (cherry picked from commit d865f635f4b2c3307e79de9be5c49ea8bd4c43a6)
  39 Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
  40 ---
  41  arch/x86/include/asm/syscalls.h |  2 +-
  42  arch/x86/kernel/ldt.c           | 16 +++++++++++++---
  43  arch/x86/um/ldt.c               |  7 +++++--
  44  3 files changed, 19 insertions(+), 6 deletions(-)
  45
  46 diff --git a/arch/x86/include/asm/syscalls.h b/arch/x86/include/asm/syscalls.h
  47 index 91dfcafe27a6..bad25bb80679 100644
  48 --- a/arch/x86/include/asm/syscalls.h
  49 +++ b/arch/x86/include/asm/syscalls.h
  50 @@ -21,7 +21,7 @@ asmlinkage long sys_ioperm(unsigned long, unsigned long, int);
  51  asmlinkage long sys_iopl(unsigned int);
  52
  53  /* kernel/ldt.c */
  54 -asmlinkage int sys_modify_ldt(int, void __user *, unsigned long);
  55 +asmlinkage long sys_modify_ldt(int, void __user *, unsigned long);
  56
  57  /* kernel/signal.c */
  58  asmlinkage long sys_rt_sigreturn(void);
  59 diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
  60 index f0e64db18ac8..0402d44deb4d 100644
  61 --- a/arch/x86/kernel/ldt.c
  62 +++ b/arch/x86/kernel/ldt.c
  63 @@ -12,6 +12,7 @@
  64  #include <linux/string.h>
  65  #include <linux/mm.h>
  66  #include <linux/smp.h>
  67 +#include <linux/syscalls.h>
  68  #include <linux/slab.h>
  69  #include <linux/vmalloc.h>
  70  #include <linux/uaccess.h>
  71 @@ -294,8 +295,8 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
  72         return error;
  73  }
  74
  75 -asmlinkage int sys_modify_ldt(int func, void __user *ptr,
  76 -                             unsigned long bytecount)
  77 +SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
  78 +               unsigned long , bytecount)
  79  {
  80         int ret = -ENOSYS;
  81
  82 @@ -313,5 +314,14 @@ asmlinkage int sys_modify_ldt(int func, void __user *ptr,
  83                 ret = write_ldt(ptr, bytecount, 0);
  84                 break;
  85         }
  86 -       return ret;
  87 +       /*
  88 +        * The SYSCALL_DEFINE() macros give us an 'unsigned long'
  89 +        * return type, but tht ABI for sys_modify_ldt() expects
  90 +        * 'int'.  This cast gives us an int-sized value in %rax
  91 +        * for the return code.  The 'unsigned' is necessary so
  92 +        * the compiler does not try to sign-extend the negative
  93 +        * return codes into the high half of the register when
  94 +        * taking the value from int->long.
  95 +        */
  96 +       return (unsigned int)ret;
  97  }
  98 diff --git a/arch/x86/um/ldt.c b/arch/x86/um/ldt.c
  99 index 836a1eb5df43..3ee234b6234d 100644
 100 --- a/arch/x86/um/ldt.c
 101 +++ b/arch/x86/um/ldt.c
 102 @@ -6,6 +6,7 @@
 103  #include <linux/mm.h>
 104  #include <linux/sched.h>
 105  #include <linux/slab.h>
 106 +#include <linux/syscalls.h>
 107  #include <linux/uaccess.h>
 108  #include <asm/unistd.h>
 109  #include <os.h>
 110 @@ -369,7 +370,9 @@ void free_ldt(struct mm_context *mm)
 111         mm->arch.ldt.entry_count = 0;
 112  }
 113
 114 -int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
 115 +SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
 116 +               unsigned long , bytecount)
 117  {
 118 -       return do_modify_ldt_skas(func, ptr, bytecount);
 119 +       /* See non-um modify_ldt() for why we do this cast */
 120 +       return (unsigned int)do_modify_ldt_skas(func, ptr, bytecount);
 121  }
 122 --
 123 2.14.2
 124