File 5b3f8fa5-port-array_index_nospec-from-Linux.patch of Package xen.8389
# Commit 2ddfae51d8b1d7b8cd33a4f6ad4d16d27cb869ae
# Date 2018-07-06 16:49:57 +0100
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Andrew Cooper <andrew.cooper3@citrix.com>
xen: Port the array_index_nospec() infrastructure from Linux
This is as the infrastructure appeared in Linux 4.17, adapted slightly for
Xen.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Julien Grall <julien.grall@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
--- a/xen/include/asm-arm/arm32/system.h
+++ b/xen/include/asm-arm/arm32/system.h
@@ -48,6 +48,24 @@ static inline int local_fiq_is_enabled(v
return !(flags & PSR_FIQ_MASK);
}
+#define CSDB ".inst 0xe320f014"
+
+static inline unsigned long array_index_mask_nospec(unsigned long idx,
+ unsigned long sz)
+{
+ unsigned long mask;
+
+ asm volatile( "cmp %1, %2\n"
+ "sbc %0, %1, %1\n"
+ CSDB
+ : "=r" (mask)
+ : "r" (idx), "Ir" (sz)
+ : "cc" );
+
+ return mask;
+}
+#define array_index_mask_nospec array_index_mask_nospec
+
#endif
/*
* Local variables:
--- a/xen/include/asm-arm/arm64/system.h
+++ b/xen/include/asm-arm/arm64/system.h
@@ -58,6 +58,28 @@ static inline int local_fiq_is_enabled(v
return !(flags & PSR_FIQ_MASK);
}
+#define csdb() asm volatile ( "hint #20" : : : "memory" )
+
+/*
+ * Generate a mask for array_index__nospec() that is ~0UL when 0 <= idx < sz
+ * and 0 otherwise.
+ */
+static inline unsigned long array_index_mask_nospec(unsigned long idx,
+ unsigned long sz)
+{
+ unsigned long mask;
+
+ asm volatile ( "cmp %1, %2\n"
+ "sbc %0, xzr, xzr\n"
+ : "=r" (mask)
+ : "r" (idx), "Ir" (sz)
+ : "cc" );
+ csdb();
+
+ return mask;
+}
+#define array_index_mask_nospec array_index_mask_nospec
+
#endif
/*
* Local variables:
--- a/xen/include/asm-x86/system.h
+++ b/xen/include/asm-x86/system.h
@@ -185,6 +185,30 @@ static always_inline unsigned long __xad
#define set_mb(var, value) do { xchg(&var, value); } while (0)
#define set_wmb(var, value) do { var = value; wmb(); } while (0)
+/**
+ * array_index_mask_nospec() - generate a mask that is ~0UL when the
+ * bounds check succeeds and 0 otherwise
+ * @index: array element index
+ * @size: number of elements in array
+ *
+ * Returns:
+ * 0 - (index < size)
+ */
+static inline unsigned long array_index_mask_nospec(unsigned long index,
+ unsigned long size)
+{
+ unsigned long mask;
+
+ asm volatile ( "cmp %[size], %[index]; sbb %[mask], %[mask];"
+ : [mask] "=r" (mask)
+ : [size] "g" (size), [index] "r" (index) );
+
+ return mask;
+}
+
+/* Override default implementation in nospec.h. */
+#define array_index_mask_nospec array_index_mask_nospec
+
#define local_irq_disable() asm volatile ( "cli" : : : "memory" )
#define local_irq_enable() asm volatile ( "sti" : : : "memory" )
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -81,6 +81,9 @@
#pragma GCC visibility push(hidden)
#endif
+/* Make the optimizer believe the variable can be manipulated arbitrarily. */
+#define OPTIMIZER_HIDE_VAR(var) __asm__ ( "" : "+g" (var) )
+
/* This macro obfuscates arithmetic on a variable address so that gcc
shouldn't recognize the original var, and make assumptions about it */
/*
--- /dev/null
+++ b/xen/include/xen/nospec.h
@@ -0,0 +1,70 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright(c) 2018 Linus Torvalds. All rights reserved. */
+/* Copyright(c) 2018 Alexei Starovoitov. All rights reserved. */
+/* Copyright(c) 2018 Intel Corporation. All rights reserved. */
+/* Copyright(c) 2018 Citrix Systems R&D Ltd. All rights reserved. */
+
+#ifndef XEN_NOSPEC_H
+#define XEN_NOSPEC_H
+
+#include <asm/system.h>
+
+/**
+ * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
+ * @index: array element index
+ * @size: number of elements in array
+ *
+ * When @index is out of bounds (@index >= @size), the sign bit will be
+ * set. Extend the sign bit to all bits and invert, giving a result of
+ * zero for an out of bounds index, or ~0 if within bounds [0, @size).
+ */
+#ifndef array_index_mask_nospec
+static inline unsigned long array_index_mask_nospec(unsigned long index,
+ unsigned long size)
+{
+ /*
+ * Always calculate and emit the mask even if the compiler
+ * thinks the mask is not needed. The compiler does not take
+ * into account the value of @index under speculation.
+ */
+ OPTIMIZER_HIDE_VAR(index);
+ return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
+}
+#endif
+
+/*
+ * array_index_nospec - sanitize an array index after a bounds check
+ *
+ * For a code sequence like:
+ *
+ * if (index < size) {
+ * index = array_index_nospec(index, size);
+ * val = array[index];
+ * }
+ *
+ * ...if the CPU speculates past the bounds check then
+ * array_index_nospec() will clamp the index within the range of [0,
+ * size).
+ */
+#define array_index_nospec(index, size) \
+({ \
+ typeof(index) _i = (index); \
+ typeof(size) _s = (size); \
+ unsigned long _mask = array_index_mask_nospec(_i, _s); \
+ \
+ BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
+ BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
+ \
+ (typeof(_i)) (_i & _mask); \
+})
+
+#endif /* XEN_NOSPEC_H */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
