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+/*
+ * Copyright © 2007,2008,2009,2010 Red Hat, Inc.
+ * Copyright © 2012,2018 Google, Inc.
+ *
+ * This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Red Hat Author(s): Behdad Esfahbod
+ * Google Author(s): Behdad Esfahbod
+ */
+
+#ifndef HB_SANITIZE_HH
+#define HB_SANITIZE_HH
+
+#include "hb.hh"
+#include "hb-blob.hh"
+#include "hb-dispatch.hh"
+
+
+/*
+ * Sanitize
+ *
+ *
+ * === Introduction ===
+ *
+ * The sanitize machinery is at the core of our zero-cost font loading. We
+ * mmap() font file into memory and create a blob out of it. Font subtables
+ * are returned as a readonly sub-blob of the main font blob. These table
+ * blobs are then sanitized before use, to ensure invalid memory access does
+ * not happen. The toplevel sanitize API use is like, eg. to load the 'head'
+ * table:
+ *
+ * hb_blob_t *head_blob = hb_sanitize_context_t ().reference_table<OT::head> (face);
+ *
+ * The blob then can be converted to a head table struct with:
+ *
+ * const head *head_table = head_blob->as<head> ();
+ *
+ * What the reference_table does is, to call hb_face_reference_table() to load
+ * the table blob, sanitize it and return either the sanitized blob, or empty
+ * blob if sanitization failed. The blob->as() function returns the null
+ * object of its template type argument if the blob is empty. Otherwise, it
+ * just casts the blob contents to the desired type.
+ *
+ * Sanitizing a blob of data with a type T works as follows (with minor
+ * simplification):
+ *
+ * - Cast blob content to T*, call sanitize() method of it,
+ * - If sanitize succeeded, return blob.
+ * - Otherwise, if blob is not writable, try making it writable,
+ * or copy if cannot be made writable in-place,
+ * - Call sanitize() again. Return blob if sanitize succeeded.
+ * - Return empty blob otherwise.
+ *
+ *
+ * === The sanitize() contract ===
+ *
+ * The sanitize() method of each object type shall return true if it's safe to
+ * call other methods of the object, and false otherwise.
+ *
+ * Note that what sanitize() checks for might align with what the specification
+ * describes as valid table data, but does not have to be. In particular, we
+ * do NOT want to be pedantic and concern ourselves with validity checks that
+ * are irrelevant to our use of the table. On the contrary, we want to be
+ * lenient with error handling and accept invalid data to the extent that it
+ * does not impose extra burden on us.
+ *
+ * Based on the sanitize contract, one can see that what we check for depends
+ * on how we use the data in other table methods. Ie. if other table methods
+ * assume that offsets do NOT point out of the table data block, then that's
+ * something sanitize() must check for (GSUB/GPOS/GDEF/etc work this way). On
+ * the other hand, if other methods do such checks themselves, then sanitize()
+ * does not have to bother with them (glyf/local work this way). The choice
+ * depends on the table structure and sanitize() performance. For example, to
+ * check glyf/loca offsets in sanitize() would cost O(num-glyphs). We try hard
+ * to avoid such costs during font loading. By postponing such checks to the
+ * actual glyph loading, we reduce the sanitize cost to O(1) and total runtime
+ * cost to O(used-glyphs). As such, this is preferred.
+ *
+ * The same argument can be made re GSUB/GPOS/GDEF, but there, the table
+ * structure is so complicated that by checking all offsets at sanitize() time,
+ * we make the code much simpler in other methods, as offsets and referenced
+ * objects do not need to be validated at each use site.
+ */
+
+/* This limits sanitizing time on really broken fonts. */
+#ifndef HB_SANITIZE_MAX_EDITS
+#define HB_SANITIZE_MAX_EDITS 32
+#endif
+#ifndef HB_SANITIZE_MAX_OPS_FACTOR
+#define HB_SANITIZE_MAX_OPS_FACTOR 8
+#endif
+#ifndef HB_SANITIZE_MAX_OPS_MIN
+#define HB_SANITIZE_MAX_OPS_MIN 16384
+#endif
+#ifndef HB_SANITIZE_MAX_OPS_MAX
+#define HB_SANITIZE_MAX_OPS_MAX 0x3FFFFFFF
+#endif
+
+struct hb_sanitize_context_t :
+ hb_dispatch_context_t<hb_sanitize_context_t, bool, HB_DEBUG_SANITIZE>
+{
+ hb_sanitize_context_t () :
+ debug_depth (0),
+ start (nullptr), end (nullptr),
+ max_ops (0),
+ writable (false), edit_count (0),
+ blob (nullptr),
+ num_glyphs (65536),
+ num_glyphs_set (false) {}
+
+ const char *get_name () { return "SANITIZE"; }
+ template <typename T, typename F>
+ bool may_dispatch (const T *obj HB_UNUSED, const F *format)
+ { return format->sanitize (this); }
+ static return_t default_return_value () { return true; }
+ static return_t no_dispatch_return_value () { return false; }
+ bool stop_sublookup_iteration (const return_t r) const { return !r; }
+
+ private:
+ template <typename T, typename ...Ts> auto
+ _dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN
+ ( obj.sanitize (this, hb_forward<Ts> (ds)...) )
+ template <typename T, typename ...Ts> auto
+ _dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN
+ ( obj.dispatch (this, hb_forward<Ts> (ds)...) )
+ public:
+ template <typename T, typename ...Ts> auto
+ dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN
+ ( _dispatch (obj, hb_prioritize, hb_forward<Ts> (ds)...) )
+
+
+ void init (hb_blob_t *b)
+ {
+ this->blob = hb_blob_reference (b);
+ this->writable = false;
+ }
+
+ void set_num_glyphs (unsigned int num_glyphs_)
+ {
+ num_glyphs = num_glyphs_;
+ num_glyphs_set = true;
+ }
+ unsigned int get_num_glyphs () { return num_glyphs; }
+
+ void set_max_ops (int max_ops_) { max_ops = max_ops_; }
+
+ template <typename T>
+ void set_object (const T *obj)
+ {
+ reset_object ();
+
+ if (!obj) return;
+
+ const char *obj_start = (const char *) obj;
+ if (unlikely (obj_start < this->start || this->end <= obj_start))
+ this->start = this->end = nullptr;
+ else
+ {
+ this->start = obj_start;
+ this->end = obj_start + hb_min (size_t (this->end - obj_start), obj->get_size ());
+ }
+ }
+
+ void reset_object ()
+ {
+ this->start = this->blob->data;
+ this->end = this->start + this->blob->length;
+ assert (this->start <= this->end); /* Must not overflow. */
+ }
+
+ void start_processing ()
+ {
+ reset_object ();
+ this->max_ops = hb_max ((unsigned int) (this->end - this->start) * HB_SANITIZE_MAX_OPS_FACTOR,
+ (unsigned) HB_SANITIZE_MAX_OPS_MIN);
+ this->edit_count = 0;
+ this->debug_depth = 0;
+
+ DEBUG_MSG_LEVEL (SANITIZE, start, 0, +1,
+ "start [%p..%p] (%lu bytes)",
+ this->start, this->end,
+ (unsigned long) (this->end - this->start));
+ }
+
+ void end_processing ()
+ {
+ DEBUG_MSG_LEVEL (SANITIZE, this->start, 0, -1,
+ "end [%p..%p] %u edit requests",
+ this->start, this->end, this->edit_count);
+
+ hb_blob_destroy (this->blob);
+ this->blob = nullptr;
+ this->start = this->end = nullptr;
+ }
+
+ unsigned get_edit_count () { return edit_count; }
+
+ bool check_range (const void *base,
+ unsigned int len) const
+ {
+ const char *p = (const char *) base;
+ bool ok = !len ||
+ (this->start <= p &&
+ p <= this->end &&
+ (unsigned int) (this->end - p) >= len &&
+ this->max_ops-- > 0);
+
+ DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
+ "check_range [%p..%p]"
+ " (%d bytes) in [%p..%p] -> %s",
+ p, p + len, len,
+ this->start, this->end,
+ ok ? "OK" : "OUT-OF-RANGE");
+
+ return likely (ok);
+ }
+
+ template <typename T>
+ bool check_range (const T *base,
+ unsigned int a,
+ unsigned int b) const
+ {
+ return !hb_unsigned_mul_overflows (a, b) &&
+ this->check_range (base, a * b);
+ }
+
+ template <typename T>
+ bool check_range (const T *base,
+ unsigned int a,
+ unsigned int b,
+ unsigned int c) const
+ {
+ return !hb_unsigned_mul_overflows (a, b) &&
+ this->check_range (base, a * b, c);
+ }
+
+ template <typename T>
+ bool check_array (const T *base, unsigned int len) const
+ {
+ return this->check_range (base, len, hb_static_size (T));
+ }
+
+ template <typename T>
+ bool check_array (const T *base,
+ unsigned int a,
+ unsigned int b) const
+ {
+ return this->check_range (base, a, b, hb_static_size (T));
+ }
+
+ template <typename Type>
+ bool check_struct (const Type *obj) const
+ { return likely (this->check_range (obj, obj->min_size)); }
+
+ bool may_edit (const void *base, unsigned int len)
+ {
+ if (this->edit_count >= HB_SANITIZE_MAX_EDITS)
+ return false;
+
+ const char *p = (const char *) base;
+ this->edit_count++;
+
+ DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
+ "may_edit(%u) [%p..%p] (%d bytes) in [%p..%p] -> %s",
+ this->edit_count,
+ p, p + len, len,
+ this->start, this->end,
+ this->writable ? "GRANTED" : "DENIED");
+
+ return this->writable;
+ }
+
+ template <typename Type, typename ValueType>
+ bool try_set (const Type *obj, const ValueType &v)
+ {
+ if (this->may_edit (obj, hb_static_size (Type)))
+ {
+ * const_cast<Type *> (obj) = v;
+ return true;
+ }
+ return false;
+ }
+
+ template <typename Type>
+ hb_blob_t *sanitize_blob (hb_blob_t *blob)
+ {
+ bool sane;
+
+ init (blob);
+
+ retry:
+ DEBUG_MSG_FUNC (SANITIZE, start, "start");
+
+ start_processing ();
+
+ if (unlikely (!start))
+ {
+ end_processing ();
+ return blob;
+ }
+
+ Type *t = reinterpret_cast<Type *> (const_cast<char *> (start));
+
+ sane = t->sanitize (this);
+ if (sane)
+ {
+ if (edit_count)
+ {
+ DEBUG_MSG_FUNC (SANITIZE, start, "passed first round with %d edits; going for second round", edit_count);
+
+ /* sanitize again to ensure no toe-stepping */
+ edit_count = 0;
+ sane = t->sanitize (this);
+ if (edit_count) {
+ DEBUG_MSG_FUNC (SANITIZE, start, "requested %d edits in second round; FAILLING", edit_count);
+ sane = false;
+ }
+ }
+ }
+ else
+ {
+ if (edit_count && !writable) {
+ start = hb_blob_get_data_writable (blob, nullptr);
+ end = start + blob->length;
+
+ if (start)
+ {
+ writable = true;
+ /* ok, we made it writable by relocating. try again */
+ DEBUG_MSG_FUNC (SANITIZE, start, "retry");
+ goto retry;
+ }
+ }
+ }
+
+ end_processing ();
+
+ DEBUG_MSG_FUNC (SANITIZE, start, sane ? "PASSED" : "FAILED");
+ if (sane)
+ {
+ hb_blob_make_immutable (blob);
+ return blob;
+ }
+ else
+ {
+ hb_blob_destroy (blob);
+ return hb_blob_get_empty ();
+ }
+ }
+
+ template <typename Type>
+ hb_blob_t *reference_table (const hb_face_t *face, hb_tag_t tableTag = Type::tableTag)
+ {
+ if (!num_glyphs_set)
+ set_num_glyphs (hb_face_get_glyph_count (face));
+ return sanitize_blob<Type> (hb_face_reference_table (face, tableTag));
+ }
+
+ mutable unsigned int debug_depth;
+ const char *start, *end;
+ mutable int max_ops;
+ private:
+ bool writable;
+ unsigned int edit_count;
+ hb_blob_t *blob;
+ unsigned int num_glyphs;
+ bool num_glyphs_set;
+};
+
+struct hb_sanitize_with_object_t
+{
+ template <typename T>
+ hb_sanitize_with_object_t (hb_sanitize_context_t *c, const T& obj) : c (c)
+ { c->set_object (obj); }
+ ~hb_sanitize_with_object_t ()
+ { c->reset_object (); }
+
+ private:
+ hb_sanitize_context_t *c;
+};
+
+
+#endif /* HB_SANITIZE_HH */
generated by cgit v1.2.3 (git 2.25.1) at 2024-04-20 02:58:40 +0000