Preserving tags
---------------
-Non-zero tags are not preserved when delivering signals. This means that
-signal handlers in applications making use of tags cannot rely on the
-tag information for user virtual addresses being maintained for fields
-inside siginfo_t. One exception to this rule is for signals raised in
-response to watchpoint debug exceptions, where the tag information will
-be preserved.
+When delivering signals, non-zero tags are not preserved in
+siginfo.si_addr unless the flag SA_EXPOSE_TAGBITS was set in
+sigaction.sa_flags when the signal handler was installed. This means
+that signal handlers in applications making use of tags cannot rely
+on the tag information for user virtual addresses being maintained
+in these fields unless the flag was set.
+
+Due to architecture limitations, bits 63:60 of the fault address
+are not preserved in response to synchronous tag check faults
+(SEGV_MTESERR) even if SA_EXPOSE_TAGBITS was set. Applications should
+treat the values of these bits as undefined in order to accommodate
+future architecture revisions which may preserve the bits.
+
+For signals raised in response to watchpoint debug exceptions, the
+tag information will be preserved regardless of the SA_EXPOSE_TAGBITS
+flag setting.
+
+Non-zero tags are never preserved in sigcontext.fault_address
+regardless of the SA_EXPOSE_TAGBITS flag setting.
The architecture prevents the use of a tagged PC, so the upper byte will
be set to a sign-extension of bit 55 on exception return.
}
asmlinkage void enter_from_user_mode(void);
-void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs);
+void do_mem_abort(unsigned long far, unsigned int esr, struct pt_regs *regs);
void do_undefinstr(struct pt_regs *regs);
void do_bti(struct pt_regs *regs);
asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr);
--- /dev/null
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARM64_ASM_SIGNAL_H
+#define __ARM64_ASM_SIGNAL_H
+
+#include <asm/memory.h>
+#include <uapi/asm/signal.h>
+#include <uapi/asm/siginfo.h>
+
+static inline void __user *arch_untagged_si_addr(void __user *addr,
+ unsigned long sig,
+ unsigned long si_code)
+{
+ /*
+ * For historical reasons, all bits of the fault address are exposed as
+ * address bits for watchpoint exceptions. New architectures should
+ * handle the tag bits consistently.
+ */
+ if (sig == SIGTRAP && si_code == TRAP_BRKPT)
+ return addr;
+
+ return untagged_addr(addr);
+}
+#define arch_untagged_si_addr arch_untagged_si_addr
+
+#endif
struct siginfo;
void arm64_notify_die(const char *str, struct pt_regs *regs,
- int signo, int sicode, void __user *addr,
+ int signo, int sicode, unsigned long far,
int err);
void hook_debug_fault_code(int nr, int (*fn)(unsigned long, unsigned int,
void unregister_undef_hook(struct undef_hook *hook);
void force_signal_inject(int signal, int code, unsigned long address, unsigned int err);
void arm64_notify_segfault(unsigned long addr);
-void arm64_force_sig_fault(int signo, int code, void __user *addr, const char *str);
-void arm64_force_sig_mceerr(int code, void __user *addr, short lsb, const char *str);
-void arm64_force_sig_ptrace_errno_trap(int errno, void __user *addr, const char *str);
+void arm64_force_sig_fault(int signo, int code, unsigned long far, const char *str);
+void arm64_force_sig_mceerr(int code, unsigned long far, short lsb, const char *str);
+void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far, const char *str);
/*
* Move regs->pc to next instruction and do necessary setup before it
if (interrupts_enabled(regs))
local_irq_enable();
- arm64_force_sig_fault(SIGTRAP, si_code,
- (void __user *)instruction_pointer(regs),
- "User debug trap");
+ arm64_force_sig_fault(SIGTRAP, si_code, instruction_pointer(regs),
+ "User debug trap");
}
static int single_step_handler(unsigned long unused, unsigned int esr,
unsigned long far = read_sysreg(far_el1);
local_daif_inherit(regs);
- far = untagged_addr(far);
do_mem_abort(far, esr, regs);
}
NOKPROBE_SYMBOL(el1_abort);
user_exit_irqoff();
local_daif_restore(DAIF_PROCCTX);
- far = untagged_addr(far);
do_mem_abort(far, esr, regs);
}
NOKPROBE_SYMBOL(el0_da);
break;
}
}
- arm64_force_sig_ptrace_errno_trap(si_errno,
- (void __user *)bkpt->trigger,
+ arm64_force_sig_ptrace_errno_trap(si_errno, bkpt->trigger,
desc);
}
#endif
- arm64_force_sig_fault(SIGTRAP, TRAP_HWBKPT,
- (void __user *)(bkpt->trigger),
- desc);
+ arm64_force_sig_fault(SIGTRAP, TRAP_HWBKPT, bkpt->trigger, desc);
}
/*
*/
long compat_arm_syscall(struct pt_regs *regs, int scno)
{
- void __user *addr;
+ unsigned long addr;
switch (scno) {
/*
break;
}
- addr = (void __user *)instruction_pointer(regs) -
- (compat_thumb_mode(regs) ? 2 : 4);
+ addr = instruction_pointer(regs) - (compat_thumb_mode(regs) ? 2 : 4);
arm64_notify_die("Oops - bad compat syscall(2)", regs,
SIGILL, ILL_ILLTRP, addr, scno);
__show_regs(regs);
}
-void arm64_force_sig_fault(int signo, int code, void __user *addr,
+void arm64_force_sig_fault(int signo, int code, unsigned long far,
const char *str)
{
arm64_show_signal(signo, str);
if (signo == SIGKILL)
force_sig(SIGKILL);
else
- force_sig_fault(signo, code, addr);
+ force_sig_fault(signo, code, (void __user *)far);
}
-void arm64_force_sig_mceerr(int code, void __user *addr, short lsb,
+void arm64_force_sig_mceerr(int code, unsigned long far, short lsb,
const char *str)
{
arm64_show_signal(SIGBUS, str);
- force_sig_mceerr(code, addr, lsb);
+ force_sig_mceerr(code, (void __user *)far, lsb);
}
-void arm64_force_sig_ptrace_errno_trap(int errno, void __user *addr,
+void arm64_force_sig_ptrace_errno_trap(int errno, unsigned long far,
const char *str)
{
arm64_show_signal(SIGTRAP, str);
- force_sig_ptrace_errno_trap(errno, addr);
+ force_sig_ptrace_errno_trap(errno, (void __user *)far);
}
void arm64_notify_die(const char *str, struct pt_regs *regs,
- int signo, int sicode, void __user *addr,
+ int signo, int sicode, unsigned long far,
int err)
{
if (user_mode(regs)) {
current->thread.fault_address = 0;
current->thread.fault_code = err;
- arm64_force_sig_fault(signo, sicode, addr, str);
+ arm64_force_sig_fault(signo, sicode, far, str);
} else {
die(str, regs, err);
}
signal = SIGKILL;
}
- arm64_notify_die(desc, regs, signal, code, (void __user *)address, err);
+ arm64_notify_die(desc, regs, signal, code, address, err);
}
/*
int code;
mmap_read_lock(current->mm);
- if (find_vma(current->mm, addr) == NULL)
+ if (find_vma(current->mm, untagged_addr(addr)) == NULL)
code = SEGV_MAPERR;
else
code = SEGV_ACCERR;
static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
{
- unsigned long address;
+ unsigned long tagged_address, address;
int rt = ESR_ELx_SYS64_ISS_RT(esr);
int crm = (esr & ESR_ELx_SYS64_ISS_CRM_MASK) >> ESR_ELx_SYS64_ISS_CRM_SHIFT;
int ret = 0;
- address = untagged_addr(pt_regs_read_reg(regs, rt));
+ tagged_address = pt_regs_read_reg(regs, rt);
+ address = untagged_addr(tagged_address);
switch (crm) {
case ESR_ELx_SYS64_ISS_CRM_DC_CVAU: /* DC CVAU, gets promoted */
}
if (ret)
- arm64_notify_segfault(address);
+ arm64_notify_segfault(tagged_address);
else
arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
}
*/
void bad_el0_sync(struct pt_regs *regs, int reason, unsigned int esr)
{
- void __user *pc = (void __user *)instruction_pointer(regs);
+ unsigned long pc = instruction_pointer(regs);
current->thread.fault_address = 0;
current->thread.fault_code = esr;
#include <asm/traps.h>
struct fault_info {
- int (*fn)(unsigned long addr, unsigned int esr,
+ int (*fn)(unsigned long far, unsigned int esr,
struct pt_regs *regs);
int sig;
int code;
current->thread.fault_code = esr;
}
-static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *regs)
+static void do_bad_area(unsigned long far, unsigned int esr,
+ struct pt_regs *regs)
{
+ unsigned long addr = untagged_addr(far);
+
/*
* If we are in kernel mode at this point, we have no context to
* handle this fault with.
const struct fault_info *inf = esr_to_fault_info(esr);
set_thread_esr(addr, esr);
- arm64_force_sig_fault(inf->sig, inf->code, (void __user *)addr,
- inf->name);
+ arm64_force_sig_fault(inf->sig, inf->code, far, inf->name);
} else {
__do_kernel_fault(addr, esr, regs);
}
return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM);
}
-static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
+static int __kprobes do_page_fault(unsigned long far, unsigned int esr,
struct pt_regs *regs)
{
const struct fault_info *inf;
vm_fault_t fault;
unsigned long vm_flags = VM_ACCESS_FLAGS;
unsigned int mm_flags = FAULT_FLAG_DEFAULT;
+ unsigned long addr = untagged_addr(far);
if (kprobe_page_fault(regs, esr))
return 0;
* We had some memory, but were unable to successfully fix up
* this page fault.
*/
- arm64_force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)addr,
- inf->name);
+ arm64_force_sig_fault(SIGBUS, BUS_ADRERR, far, inf->name);
} else if (fault & (VM_FAULT_HWPOISON_LARGE | VM_FAULT_HWPOISON)) {
unsigned int lsb;
if (fault & VM_FAULT_HWPOISON_LARGE)
lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
- arm64_force_sig_mceerr(BUS_MCEERR_AR, (void __user *)addr, lsb,
- inf->name);
+ arm64_force_sig_mceerr(BUS_MCEERR_AR, far, lsb, inf->name);
} else {
/*
* Something tried to access memory that isn't in our memory
*/
arm64_force_sig_fault(SIGSEGV,
fault == VM_FAULT_BADACCESS ? SEGV_ACCERR : SEGV_MAPERR,
- (void __user *)addr,
- inf->name);
+ far, inf->name);
}
return 0;
return 0;
}
-static int __kprobes do_translation_fault(unsigned long addr,
+static int __kprobes do_translation_fault(unsigned long far,
unsigned int esr,
struct pt_regs *regs)
{
+ unsigned long addr = untagged_addr(far);
+
if (is_ttbr0_addr(addr))
- return do_page_fault(addr, esr, regs);
+ return do_page_fault(far, esr, regs);
- do_bad_area(addr, esr, regs);
+ do_bad_area(far, esr, regs);
return 0;
}
-static int do_alignment_fault(unsigned long addr, unsigned int esr,
+static int do_alignment_fault(unsigned long far, unsigned int esr,
struct pt_regs *regs)
{
- do_bad_area(addr, esr, regs);
+ do_bad_area(far, esr, regs);
return 0;
}
-static int do_bad(unsigned long addr, unsigned int esr, struct pt_regs *regs)
+static int do_bad(unsigned long far, unsigned int esr, struct pt_regs *regs)
{
return 1; /* "fault" */
}
-static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
+static int do_sea(unsigned long far, unsigned int esr, struct pt_regs *regs)
{
const struct fault_info *inf;
- void __user *siaddr;
+ unsigned long siaddr;
inf = esr_to_fault_info(esr);
return 0;
}
- if (esr & ESR_ELx_FnV)
- siaddr = NULL;
- else
- siaddr = (void __user *)addr;
+ if (esr & ESR_ELx_FnV) {
+ siaddr = 0;
+ } else {
+ /*
+ * The architecture specifies that the tag bits of FAR_EL1 are
+ * UNKNOWN for synchronous external aborts. Mask them out now
+ * so that userspace doesn't see them.
+ */
+ siaddr = untagged_addr(far);
+ }
arm64_notify_die(inf->name, regs, inf->sig, inf->code, siaddr, esr);
return 0;
}
-static int do_tag_check_fault(unsigned long addr, unsigned int esr,
+static int do_tag_check_fault(unsigned long far, unsigned int esr,
struct pt_regs *regs)
{
- do_bad_area(addr, esr, regs);
+ /*
+ * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN for tag
+ * check faults. Mask them out now so that userspace doesn't see them.
+ */
+ far &= (1UL << 60) - 1;
+ do_bad_area(far, esr, regs);
return 0;
}
{ do_bad, SIGKILL, SI_KERNEL, "unknown 63" },
};
-void do_mem_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs)
+void do_mem_abort(unsigned long far, unsigned int esr, struct pt_regs *regs)
{
const struct fault_info *inf = esr_to_fault_info(esr);
+ unsigned long addr = untagged_addr(far);
- if (!inf->fn(addr, esr, regs))
+ if (!inf->fn(far, esr, regs))
return;
if (!user_mode(regs)) {
show_pte(addr);
}
- arm64_notify_die(inf->name, regs,
- inf->sig, inf->code, (void __user *)addr, esr);
+ /*
+ * At this point we have an unrecognized fault type whose tag bits may
+ * have been defined as UNKNOWN. Therefore we only expose the untagged
+ * address to the signal handler.
+ */
+ arm64_notify_die(inf->name, regs, inf->sig, inf->code, addr, esr);
}
NOKPROBE_SYMBOL(do_mem_abort);
void do_sp_pc_abort(unsigned long addr, unsigned int esr, struct pt_regs *regs)
{
- arm64_notify_die("SP/PC alignment exception", regs,
- SIGBUS, BUS_ADRALN, (void __user *)addr, esr);
+ arm64_notify_die("SP/PC alignment exception", regs, SIGBUS, BUS_ADRALN,
+ addr, esr);
}
NOKPROBE_SYMBOL(do_sp_pc_abort);
arm64_apply_bp_hardening();
if (inf->fn(addr_if_watchpoint, esr, regs)) {
- arm64_notify_die(inf->name, regs,
- inf->sig, inf->code, (void __user *)pc, esr);
+ arm64_notify_die(inf->name, regs, inf->sig, inf->code, pc, esr);
}
debug_exception_exit(regs);