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/*
* Copyright (C) 2020 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#pragma once
#include <stddef.h>
#include <sys/prctl.h>
inline uintptr_t __bionic_clear_pac_bits(uintptr_t ptr) {
#if defined(__aarch64__)
register uintptr_t x30 __asm("x30") = ptr;
// This is a NOP on pre-Armv8.3-A architectures.
asm("xpaclri" : "+r"(x30));
return x30;
#else
return ptr;
#endif
}
#ifdef __aarch64__
// The default setting for branch-protection enables both PAC and BTI, so by
// overriding it to only enable BTI we disable PAC.
#define __BIONIC_DISABLE_PAUTH __attribute__((target("branch-protection=bti")))
#else
#define __BIONIC_DISABLE_PAUTH
#endif
#ifdef __aarch64__
#ifndef PR_PAC_SET_ENABLED_KEYS
#define PR_PAC_SET_ENABLED_KEYS 60
#endif
#ifndef PR_PAC_GET_ENABLED_KEYS
#define PR_PAC_GET_ENABLED_KEYS 61
#endif
// Disable PAC (i.e. make the signing and authentication instructions into no-ops) for the lifetime
// of this object.
class ScopedDisablePAC {
int prev_enabled_keys_;
public:
// Disabling IA will invalidate the return address in this function if it is signed, so we need to
// make sure that this function does not sign its return address. Likewise for the destructor.
__BIONIC_DISABLE_PAUTH
ScopedDisablePAC() {
// These prctls will fail (resulting in a no-op, the intended behavior) if PAC is not supported.
prev_enabled_keys_ = prctl(PR_PAC_GET_ENABLED_KEYS, 0, 0, 0, 0);
prctl(PR_PAC_SET_ENABLED_KEYS, prev_enabled_keys_, 0, 0, 0);
}
__BIONIC_DISABLE_PAUTH
~ScopedDisablePAC() {
prctl(PR_PAC_SET_ENABLED_KEYS, prev_enabled_keys_, prev_enabled_keys_, 0, 0);
}
};
#else
struct ScopedDisablePAC {
// Silence unused variable warnings in non-aarch64 builds.
ScopedDisablePAC() {}
};
#endif
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