lkml.org 
[lkml]   [2018]   [Jan]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH v2 05/19] x86: implement ifence_array_ptr() and array_ptr_mask()
From
Date
'ifence_array_ptr' is provided as an alternative to the default
'__array_ptr' implementation that uses a mask to sanitize user
controllable pointers. Later patches will allow it to be selected via
kernel command line. The '__array_ptr' implementation otherwise appears
safe for current generation cpus across multiple architectures.

'array_ptr_mask' is used by the default 'array_ptr' implementation to
cheaply calculate an array bounds mask.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
arch/x86/include/asm/barrier.h | 42 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)

diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
index b04f572d6d97..4450d25d8cde 100644
--- a/arch/x86/include/asm/barrier.h
+++ b/arch/x86/include/asm/barrier.h
@@ -28,6 +28,48 @@
#define ifence() alternative_2("", "mfence", X86_FEATURE_MFENCE_RDTSC, \
"lfence", X86_FEATURE_LFENCE_RDTSC)

+/**
+ * ifence_array_ptr - Generate a pointer to an array element,
+ * ensuring the pointer is bounded under speculation.
+ *
+ * @arr: the base of the array
+ * @idx: the index of the element
+ * @sz: the number of elements in the array
+ *
+ * If @idx falls in the interval [0, @sz), returns the pointer to
+ * @arr[@idx], otherwise returns NULL.
+ */
+#define ifence_array_ptr(arr, idx, sz) \
+({ \
+ typeof(*(arr)) *__arr = (arr), *__ret; \
+ typeof(idx) __idx = (idx); \
+ typeof(sz) __sz = (sz); \
+ \
+ __ret = __idx < __sz ? __arr + __idx : NULL; \
+ ifence(); \
+ __ret; \
+})
+
+/**
+ * array_ptr_mask - generate a mask for array_ptr() that is ~0UL when
+ * the bounds check succeeds and 0 otherwise
+ */
+#define array_ptr_mask array_ptr_mask
+static inline unsigned long array_ptr_mask(unsigned long idx, unsigned long sz)
+{
+ unsigned long mask;
+
+ /*
+ * mask = index - size, if that result is >= 0 then the index is
+ * invalid and the mask is 0 else ~0
+ */
+ asm ("cmpq %1,%2; sbbq %0,%0;"
+ :"=r" (mask)
+ :"r"(sz),"r" (idx)
+ :"cc");
+ return mask;
+}
+
#ifdef CONFIG_X86_PPRO_FENCE
#define dma_rmb() rmb()
#else
\
 
 \ /
  Last update: 2018-01-14 23:25    [W:0.158 / U:2.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site