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Revert "Disable pointer authentication in app processes."

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Revert "[automerged blank] Disable pointer authentication in app..."

Revert submission 16712509-sc-dev-I3030c47be9d02a27505bd4775c1982a20755758c-sc-v2-dev

Reason for revert: PAC has shipped with S, and we're going with app compat outreach rather than regressing security.
Reverted Changes:
I3030c47be:Disable pointer authentication in app processes.
I3030c47be:Disable pointer authentication in app processes.
I84a696428:[automerged blank] Disable pointer authentication ...
Ibc52deaf3:[automerged blank] Disable pointer authentication ...

Change-Id: I637d453a5b137841bcb794264b6f6c393fb924da
This commit is contained in:
Elliott Hughes 2022-03-16 02:35:10 +00:00
parent b81b50bf2c
commit af2f109a9c
2 changed files with 3 additions and 48 deletions
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5
libc/bionic/pthread_create.cpp
View file

@ -45,7 +45,6 @@
#include "private/bionic_defs.h"
#include "private/bionic_globals.h"
#include "platform/bionic/macros.h"
#include "platform/bionic/pac.h"
#include "private/bionic_ssp.h"
#include "private/bionic_systrace.h"
#include "private/bionic_tls.h"
@ -332,9 +331,11 @@ void __set_stack_and_tls_vma_name(bool is_main_thread) {
extern "C" int __rt_sigprocmask(int, const sigset64_t*, sigset64_t*, size_t);
__attribute__((no_sanitize("hwaddress")))
#ifdef __aarch64__
// This function doesn't return, but it does appear in stack traces. Avoid using return PAC in this
// function because we may end up resetting IA, which may confuse unwinders due to mismatching keys.
__BIONIC_DISABLE_PAUTH
__attribute__((target("branch-protection=bti")))
#endif
static int __pthread_start(void* arg) {
pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg);

46
libc/platform/bionic/pac.h
View file

@ -29,7 +29,6 @@
#pragma once
#include <stddef.h>
#include <sys/prctl.h>
inline uintptr_t __bionic_clear_pac_bits(uintptr_t ptr) {
#if defined(__aarch64__)
@ -41,48 +40,3 @@ inline uintptr_t __bionic_clear_pac_bits(uintptr_t ptr) {
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