diff mbox

x86/CET: Renumber ARCH_CET_LEGACY_BITMAP to 0x3006

Message ID 20181120142214.20783-1-hjl.tools@gmail.com
State New, archived
Headers

Commit Message

H.J. Lu Nov. 20, 2018, 2:22 p.m. UTC 
  The current CET kernel:

https://github.com/yyu168/linux_cet

changed legacy region bitmap allocation from kernel to user space and
renumbered the prctl number from 0x3005 to 0x3006.  This patch updates
glibc with:

/* Enable legacy region bitmap with unsigned long long *addr:
     address: addr[0].
     size: addr[1].
 */
 # define ARCH_CET_LEGACY_BITMAP	0x3006

	* sysdeps/unix/sysv/linux/x86/dl-cet.h
	(dl_cet_allocate_legacy_bitmap ): Removed.
	(dl_cet_enable_legacy_bitmap): New.
	* sysdeps/unix/sysv/linux/x86/include/asm/prctl.h
	(ARCH_CET_LEGACY_BITMAP): Renumbered to 0x3006.
	* sysdeps/x86/dl-cet.c (dl_cet_check): Mmap legacy bitmap.
	Call dl_cet_enable_legacy_bitmap instead of
	dl_cet_allocate_legacy_bitmap.
---
 sysdeps/unix/sysv/linux/x86/dl-cet.h          | 17 +++++-------
 .../unix/sysv/linux/x86/include/asm/prctl.h   |  4 +--
 sysdeps/x86/dl-cet.c                          | 27 ++++++++++++++++---
 3 files changed, 32 insertions(+), 16 deletions(-)

Comments

Florian Weimer Nov. 20, 2018, 4:07 p.m. UTC | #1 
* H. J. Lu:

> The current CET kernel:
>
> https://github.com/yyu168/linux_cet
>
> changed legacy region bitmap allocation from kernel to user space and
> renumbered the prctl number from 0x3005 to 0x3006.  This patch updates
> glibc with:
>
> /* Enable legacy region bitmap with unsigned long long *addr:
>      address: addr[0].
>      size: addr[1].
>  */
>  # define ARCH_CET_LEGACY_BITMAP	0x3006

The patch looks okay in general, but I suggest to wait until this is
actually merged into an upstream kernel, so that we don't have to change
the number again.

> +		  /* Allocate and enable legacy bitmap.  */
> +		  size_t legacy_bitmap_size
> +		    = ((uintptr_t) __libc_stack_end
> +		       / GLRO(dl_pagesize) / 8);
> +		  void *legacy_bitmap_addr
> +		    = __mmap (NULL, legacy_bitmap_size,
> +			      PROT_READ | PROT_WRITE,
> +			      MAP_ANON | MAP_PRIVATE | MAP_NORESERVE,
> +			      -1, 0);
> +		  if (legacy_bitmap_addr == MAP_FAILED)
> +		    {
> +		      if (program)
> +			_dl_fatal_printf ("%s: mmap legacy bitmap failed\n",
> +					  l->l_name);
> +		      else
> +			_dl_signal_error (EINVAL, l->l_name, "dlopen",
> +					  N_("mmap legacy bitmap failed"));

Maybe you can log the size of the mapping attempt?  That could be useful
to diagnose failures.

Thanks,
Florian
H.J. Lu Nov. 21, 2018, 10:37 p.m. UTC | #2 
On Tue, Nov 20, 2018 at 8:07 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > The current CET kernel:
> >
> > https://github.com/yyu168/linux_cet
> >
> > changed legacy region bitmap allocation from kernel to user space and
> > renumbered the prctl number from 0x3005 to 0x3006.  This patch updates
> > glibc with:
> >
> > /* Enable legacy region bitmap with unsigned long long *addr:
> >      address: addr[0].
> >      size: addr[1].
> >  */
> >  # define ARCH_CET_LEGACY_BITMAP      0x3006
>
> The patch looks okay in general, but I suggest to wait until this is
> actually merged into an upstream kernel, so that we don't have to change
> the number again.

Sure.

> > +               /* Allocate and enable legacy bitmap.  */
> > +               size_t legacy_bitmap_size
> > +                 = ((uintptr_t) __libc_stack_end
> > +                    / GLRO(dl_pagesize) / 8);
> > +               void *legacy_bitmap_addr
> > +                 = __mmap (NULL, legacy_bitmap_size,
> > +                           PROT_READ | PROT_WRITE,
> > +                           MAP_ANON | MAP_PRIVATE | MAP_NORESERVE,
> > +                           -1, 0);
> > +               if (legacy_bitmap_addr == MAP_FAILED)
> > +                 {
> > +                   if (program)
> > +                     _dl_fatal_printf ("%s: mmap legacy bitmap failed\n",
> > +                                       l->l_name);
> > +                   else
> > +                     _dl_signal_error (EINVAL, l->l_name, "dlopen",
> > +                                       N_("mmap legacy bitmap failed"));
>
> Maybe you can log the size of the mapping attempt?  That could be useful
> to diagnose failures.

It isn't easy since  _dl_signal_error only takes strings.
Florian Weimer Nov. 21, 2018, 11:02 p.m. UTC | #3 
* H. J. Lu:

>> Maybe you can log the size of the mapping attempt?  That could be useful
>> to diagnose failures.
>
> It isn't easy since  _dl_signal_error only takes strings.

Ah.  We have _dl_exception_create_format and _dl_signal_exception for
that; this functionality is split across two function.

Thanks,
Florian
diff mbox

Patch

diff --git a/sysdeps/unix/sysv/linux/x86/dl-cet.h b/sysdeps/unix/sysv/linux/x86/dl-cet.h
index 3fbcfebed5..4da8d165dc 100644
--- a/sysdeps/unix/sysv/linux/x86/dl-cet.h
+++ b/sysdeps/unix/sysv/linux/x86/dl-cet.h
@@ -19,24 +19,19 @@ 
 #include <asm/prctl.h>
 
 static inline int __attribute__ ((always_inline))
-dl_cet_allocate_legacy_bitmap (unsigned long *legacy_bitmap)
+dl_cet_enable_legacy_bitmap (unsigned long *legacy_bitmap)
 {
   /* Allocate legacy bitmap.  */
   INTERNAL_SYSCALL_DECL (err);
 #ifdef __LP64__
-  return (int) INTERNAL_SYSCALL (arch_prctl, err, 2,
-				 ARCH_CET_LEGACY_BITMAP, legacy_bitmap);
+  unsigned long *legacy_bitmap_u64 = legacy_bitmap;
 #else
   unsigned long long legacy_bitmap_u64[2];
-  int res = INTERNAL_SYSCALL (arch_prctl, err, 2,
-			      ARCH_CET_LEGACY_BITMAP, legacy_bitmap_u64);
-  if (res == 0)
-    {
-      legacy_bitmap[0] = legacy_bitmap_u64[0];
-      legacy_bitmap[1] = legacy_bitmap_u64[1];
-    }
-  return res;
+  legacy_bitmap_u64[0] = legacy_bitmap[0];
+  legacy_bitmap_u64[1] = legacy_bitmap[1];
 #endif
+  return (int) INTERNAL_SYSCALL (arch_prctl, err, 2,
+				 ARCH_CET_LEGACY_BITMAP, legacy_bitmap_u64);
 }
 
 static inline int __attribute__ ((always_inline))
diff --git a/sysdeps/unix/sysv/linux/x86/include/asm/prctl.h b/sysdeps/unix/sysv/linux/x86/include/asm/prctl.h
index f67f3299b9..94196aa768 100644
--- a/sysdeps/unix/sysv/linux/x86/include/asm/prctl.h
+++ b/sysdeps/unix/sysv/linux/x86/include/asm/prctl.h
@@ -24,9 +24,9 @@ 
      OUT: allocated shadow stack address: *addr.
  */
 # define ARCH_CET_ALLOC_SHSTK	0x3004
-/* Return legacy region bitmap info in unsigned long long *addr:
+/* Enable legacy region bitmap with unsigned long long *addr:
      address: addr[0].
      size: addr[1].
  */
-# define ARCH_CET_LEGACY_BITMAP	0x3005
+# define ARCH_CET_LEGACY_BITMAP	0x3006
 #endif /* ARCH_CET_STATUS */
diff --git a/sysdeps/x86/dl-cet.c b/sysdeps/x86/dl-cet.c
index 78f36bcf53..983caa0018 100644
--- a/sysdeps/x86/dl-cet.c
+++ b/sysdeps/x86/dl-cet.c
@@ -202,13 +202,34 @@  mprotect_failure:
 					  N_("mprotect legacy bitmap failed"));
 		    }
 		}
-	      else
+	      else if (!GL(dl_x86_legacy_bitmap)[0])
 		{
-		  /* Allocate legacy bitmap.  */
-		  int res = dl_cet_allocate_legacy_bitmap
+		  /* Allocate and enable legacy bitmap.  */
+		  size_t legacy_bitmap_size
+		    = ((uintptr_t) __libc_stack_end
+		       / GLRO(dl_pagesize) / 8);
+		  void *legacy_bitmap_addr
+		    = __mmap (NULL, legacy_bitmap_size,
+			      PROT_READ | PROT_WRITE,
+			      MAP_ANON | MAP_PRIVATE | MAP_NORESERVE,
+			      -1, 0);
+		  if (legacy_bitmap_addr == MAP_FAILED)
+		    {
+		      if (program)
+			_dl_fatal_printf ("%s: mmap legacy bitmap failed\n",
+					  l->l_name);
+		      else
+			_dl_signal_error (EINVAL, l->l_name, "dlopen",
+					  N_("mmap legacy bitmap failed"));
+		    }
+		  GL(dl_x86_legacy_bitmap)[0]
+		    = (uintptr_t) legacy_bitmap_addr;
+		  GL(dl_x86_legacy_bitmap)[1] = legacy_bitmap_size;
+		  int res = dl_cet_enable_legacy_bitmap
 		    (GL(dl_x86_legacy_bitmap));
 		  if (res != 0)
 		    {
+		      __munmap (legacy_bitmap_addr, legacy_bitmap_size);
 		      if (program)
 			_dl_fatal_printf ("%s: legacy bitmap isn't available\n",
 					  l->l_name);