arm64: expose FAR_EL1 tag bits in siginfo

The kernel currently clears the tag bits (i.e. bits 56-63) in the fault
address exposed via siginfo.si_addr and sigcontext.fault_address. However,
the tag bits may be needed by tools in order to accurately diagnose
memory errors, such as HWASan [1] or future tools based on the Memory
Tagging Extension (MTE).

Expose these bits via the arch_untagged_si_addr mechanism, so that
they are only exposed to signal handlers with the SA_EXPOSE_TAGBITS
flag set.

[1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

Signed-off-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://linux-review.googlesource.com/id/Ia8876bad8c798e0a32df7c2ce1256c4771c81446
Link: https://lore.kernel.org/r/0010296597784267472fa13b39f8238d87a72cf8.1605904350.git.pcc@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 15 insertions, 14 deletions

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 8af4e0e85736..f4ddbe9ed3f1 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -170,32 +170,32 @@ static void arm64_show_signal(int signo, const char *str)
 	__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)) {
@@ -203,7 +203,7 @@ void arm64_notify_die(const char *str, struct pt_regs *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);
 	}
@@ -374,7 +374,7 @@ void force_signal_inject(int signal, int code, unsigned long address, unsigned i
 		signal = SIGKILL;
 	}
 
-	arm64_notify_die(desc, regs, signal, code, (void __user *)address, err);
+	arm64_notify_die(desc, regs, signal, code, address, err);
 }
 
 /*
@@ -385,7 +385,7 @@ void arm64_notify_segfault(unsigned long addr)
 	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;
@@ -448,12 +448,13 @@ NOKPROBE_SYMBOL(do_ptrauth_fault);
 
 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 */
@@ -480,7 +481,7 @@ static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
 	}
 
 	if (ret)
-		arm64_notify_segfault(address);
+		arm64_notify_segfault(tagged_address);
 	else
 		arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
 }
@@ -772,7 +773,7 @@ asmlinkage void bad_mode(struct pt_regs *regs, int reason, unsigned int esr)
  */
 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;