x86 ptrace: unify syscall tracing

This unifies and cleans up the syscall tracing code on i386 and x86_64.

Using a single function for entry and exit tracing on 32-bit made the
do_syscall_trace() into some terrible spaghetti.  The logic is clear and
simple using separate syscall_trace_enter() and syscall_trace_leave()
functions as on 64-bit.

The unification adds PTRACE_SYSEMU and PTRACE_SYSEMU_SINGLESTEP support
on x86_64, for 32-bit ptrace() callers and for 64-bit ptrace() callers
tracing either 32-bit or 64-bit tasks.  It behaves just like 32-bit.

Changing syscall_trace_enter() to return the syscall number shortens
all the assembly paths, while adding the SYSEMU feature in a simple way.

Signed-off-by: Roland McGrath <roland@redhat.com>

3 files changed, 62 insertions, 112 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 0ad987d02b7..cadf73f70d3 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -332,7 +332,7 @@ sysenter_past_esp:
         GET_THREAD_INFO(%ebp)
 
         /* Note, _TIF_SECCOMP is bit number 8, and so it needs testw and not testb */
-        testw $(_TIF_SYSCALL_EMU|_TIF_SYSCALL_TRACE|_TIF_SECCOMP|_TIF_SYSCALL_AUDIT),TI_flags(%ebp)
+        testw $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%ebp)
         jnz syscall_trace_entry
         cmpl $(nr_syscalls), %eax
         jae syscall_badsys
@@ -370,7 +370,7 @@ ENTRY(system_call)
         GET_THREAD_INFO(%ebp)
                                         # system call tracing in operation / emulation
         /* Note, _TIF_SECCOMP is bit number 8, and so it needs testw and not testb */
-        testw $(_TIF_SYSCALL_EMU|_TIF_SYSCALL_TRACE|_TIF_SECCOMP|_TIF_SYSCALL_AUDIT),TI_flags(%ebp)
+        testw $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%ebp)
         jnz syscall_trace_entry
         cmpl $(nr_syscalls), %eax
         jae syscall_badsys
@@ -510,12 +510,8 @@ END(work_pending)
 syscall_trace_entry:
         movl $-ENOSYS,PT_EAX(%esp)
         movl %esp, %eax
-        xorl %edx,%edx
-        call do_syscall_trace
-        cmpl $0, %eax
-        jne resume_userspace            # ret != 0 -> running under PTRACE_SYSEMU,
-                                        # so must skip actual syscall
-        movl PT_ORIG_EAX(%esp), %eax
+        call syscall_trace_enter
+        /* What it returned is what we'll actually use.  */
         cmpl $(nr_syscalls), %eax
         jnae syscall_call
         jmp syscall_exit
@@ -524,14 +520,13 @@ END(syscall_trace_entry)
         # perform syscall exit tracing
         ALIGN
 syscall_exit_work:
-        testb $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP), %cl
+        testb $_TIF_WORK_SYSCALL_EXIT, %cl
         jz work_pending
         TRACE_IRQS_ON
-        ENABLE_INTERRUPTS(CLBR_ANY)     # could let do_syscall_trace() call
+        ENABLE_INTERRUPTS(CLBR_ANY)     # could let syscall_trace_leave() call
                                         # schedule() instead
         movl %esp, %eax
-        movl $1, %edx
-        call do_syscall_trace
+        call syscall_trace_leave
         jmp resume_userspace
 END(syscall_exit_work)
         CFI_ENDPROC
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index ae63e584c34..63001c6ecf6 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -349,8 +349,7 @@ ENTRY(system_call_after_swapgs)
         movq  %rcx,RIP-ARGOFFSET(%rsp)
         CFI_REL_OFFSET rip,RIP-ARGOFFSET
         GET_THREAD_INFO(%rcx)
-        testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP), \
-                TI_flags(%rcx)
+        testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%rcx)
         jnz tracesys
         cmpq $__NR_syscall_max,%rax
         ja badsys
@@ -430,7 +429,12 @@ tracesys:
         FIXUP_TOP_OF_STACK %rdi
         movq %rsp,%rdi
         call syscall_trace_enter
-        LOAD_ARGS ARGOFFSET  /* reload args from stack in case ptrace changed it */
+        /*
+         * Reload arg registers from stack in case ptrace changed them.
+         * We don't reload %rax because syscall_trace_enter() returned
+         * the value it wants us to use in the table lookup.
+         */
+        LOAD_ARGS ARGOFFSET, 1
         RESTORE_REST
         cmpq $__NR_syscall_max,%rax
         ja   int_ret_from_sys_call      /* RAX(%rsp) set to -ENOSYS above */
@@ -483,7 +487,7 @@ int_very_careful:
         ENABLE_INTERRUPTS(CLBR_NONE)
         SAVE_REST
         /* Check for syscall exit trace */      
-        testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP),%edx
+        testl $_TIF_WORK_SYSCALL_EXIT,%edx
         jz int_signal
         pushq %rdi
         CFI_ADJUST_CFA_OFFSET 8
@@ -491,7 +495,7 @@ int_very_careful:
         call syscall_trace_leave
         popq %rdi
         CFI_ADJUST_CFA_OFFSET -8
-        andl $~(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP),%edi
+        andl $~(_TIF_WORK_SYSCALL_EXIT|_TIF_SYSCALL_EMU),%edi
         jmp int_restore_rest
         
 int_signal:
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 77040b6070e..34e77b16a42 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1357,8 +1357,6 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task)
 #endif
 }
 
-#ifdef CONFIG_X86_32
-
 void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code)
 {
         struct siginfo info;
@@ -1377,89 +1375,10 @@ void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code)
         force_sig_info(SIGTRAP, &info, tsk);
 }
 
-/* notification of system call entry/exit
- * - triggered by current->work.syscall_trace
- */
-int do_syscall_trace(struct pt_regs *regs, int entryexit)
-{
-        int is_sysemu = test_thread_flag(TIF_SYSCALL_EMU);
-        /*
-         * With TIF_SYSCALL_EMU set we want to ignore TIF_SINGLESTEP for syscall
-         * interception
-         */
-        int is_singlestep = !is_sysemu && test_thread_flag(TIF_SINGLESTEP);
-        int ret = 0;
-
-        /* do the secure computing check first */
-        if (!entryexit)
-                secure_computing(regs->orig_ax);
-
-        if (unlikely(current->audit_context)) {
-                if (entryexit)
-                        audit_syscall_exit(AUDITSC_RESULT(regs->ax),
-                                                regs->ax);
-                /* Debug traps, when using PTRACE_SINGLESTEP, must be sent only
-                 * on the syscall exit path. Normally, when TIF_SYSCALL_AUDIT is
-                 * not used, entry.S will call us only on syscall exit, not
-                 * entry; so when TIF_SYSCALL_AUDIT is used we must avoid
-                 * calling send_sigtrap() on syscall entry.
-                 *
-                 * Note that when PTRACE_SYSEMU_SINGLESTEP is used,
-                 * is_singlestep is false, despite his name, so we will still do
-                 * the correct thing.
-                 */
-                else if (is_singlestep)
-                        goto out;
-        }
-
-        if (!(current->ptrace & PT_PTRACED))
-                goto out;
-
-        /* If a process stops on the 1st tracepoint with SYSCALL_TRACE
-         * and then is resumed with SYSEMU_SINGLESTEP, it will come in
-         * here. We have to check this and return */
-        if (is_sysemu && entryexit)
-                return 0;
-
-        /* Fake a debug trap */
-        if (is_singlestep)
-                send_sigtrap(current, regs, 0);
-
-        if (!test_thread_flag(TIF_SYSCALL_TRACE) && !is_sysemu)
-                goto out;
-
-        /* the 0x80 provides a way for the tracing parent to distinguish
-           between a syscall stop and SIGTRAP delivery */
-        /* Note that the debugger could change the result of test_thread_flag!*/
-        ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD) ? 0x80:0));
-
-        /*
-         * this isn't the same as continuing with a signal, but it will do
-         * for normal use.  strace only continues with a signal if the
-         * stopping signal is not SIGTRAP.  -brl
-         */
-        if (current->exit_code) {
-                send_sig(current->exit_code, current, 1);
-                current->exit_code = 0;
-        }
-        ret = is_sysemu;
-out:
-        if (unlikely(current->audit_context) && !entryexit)
-                audit_syscall_entry(AUDIT_ARCH_I386, regs->orig_ax,
-                                    regs->bx, regs->cx, regs->dx, regs->si);
-        if (ret == 0)
-                return 0;
-
-        regs->orig_ax = -1; /* force skip of syscall restarting */
-        if (unlikely(current->audit_context))
-                audit_syscall_exit(AUDITSC_RESULT(regs->ax), regs->ax);
-        return 1;
-}
-
-#else  /* CONFIG_X86_64 */
-
 static void syscall_trace(struct pt_regs *regs)
 {
+        if (!(current->ptrace & PT_PTRACED))
+                return;
 
 #if 0
         printk("trace %s ip %lx sp %lx ax %d origrax %d caller %lx tiflags %x ptrace %x\n",
@@ -1481,39 +1400,71 @@ static void syscall_trace(struct pt_regs *regs)
         }
 }
 
-asmlinkage void syscall_trace_enter(struct pt_regs *regs)
+#ifdef CONFIG_X86_32
+# define IS_IA32        1
+#elif defined CONFIG_IA32_EMULATION
+# define IS_IA32        test_thread_flag(TIF_IA32)
+#else
+# define IS_IA32        0
+#endif
+
+/*
+ * We must return the syscall number to actually look up in the table.
+ * This can be -1L to skip running any syscall at all.
+ */
+asmregparm long syscall_trace_enter(struct pt_regs *regs)
 {
+        long ret = 0;
+
         /* do the secure computing check first */
         secure_computing(regs->orig_ax);
 
-        if (test_thread_flag(TIF_SYSCALL_TRACE)
-            && (current->ptrace & PT_PTRACED))
+        if (unlikely(test_thread_flag(TIF_SYSCALL_EMU)))
+                ret = -1L;
+
+        if (ret || test_thread_flag(TIF_SYSCALL_TRACE))
                 syscall_trace(regs);
 
         if (unlikely(current->audit_context)) {
-                if (test_thread_flag(TIF_IA32)) {
+                if (IS_IA32)
                         audit_syscall_entry(AUDIT_ARCH_I386,
                                             regs->orig_ax,
                                             regs->bx, regs->cx,
                                             regs->dx, regs->si);
-                } else {
+#ifdef CONFIG_X86_64
+                else
                         audit_syscall_entry(AUDIT_ARCH_X86_64,
                                             regs->orig_ax,
                                             regs->di, regs->si,
                                             regs->dx, regs->r10);
-                }
+#endif
         }
+
+        return ret ?: regs->orig_ax;
 }
 
-asmlinkage void syscall_trace_leave(struct pt_regs *regs)
+asmregparm void syscall_trace_leave(struct pt_regs *regs)
 {
         if (unlikely(current->audit_context))
                 audit_syscall_exit(AUDITSC_RESULT(regs->ax), regs->ax);
 
-        if ((test_thread_flag(TIF_SYSCALL_TRACE)
-             || test_thread_flag(TIF_SINGLESTEP))
-            && (current->ptrace & PT_PTRACED))
+        if (test_thread_flag(TIF_SYSCALL_TRACE))
                 syscall_trace(regs);
-}
 
-#endif  /* CONFIG_X86_32 */
+        /*
+         * If TIF_SYSCALL_EMU is set, we only get here because of
+         * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
+         * We already reported this syscall instruction in
+         * syscall_trace_enter(), so don't do any more now.
+         */
+        if (unlikely(test_thread_flag(TIF_SYSCALL_EMU)))
+                return;
+
+        /*
+         * If we are single-stepping, synthesize a trap to follow the
+         * system call instruction.
+         */
+        if (test_thread_flag(TIF_SINGLESTEP) &&
+            (current->ptrace & PT_PTRACED))
+                send_sigtrap(current, regs, 0);
+}