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authorOleg Nesterov <oleg@redhat.com>2021-02-01 18:47:09 +0100
committerThomas Gleixner <tglx@linutronix.de>2021-03-16 22:13:11 +0100
commit8c150ba2fb5995c84a7a43848250d444a3329a7d (patch)
tree711ea8a4125668f0749c8f0692a258585dec00a0
parent66c1b6d74cd7035e85c426f0af4aede19e805c8a (diff)
downloadlinux-stericsson-8c150ba2fb5995c84a7a43848250d444a3329a7d.tar.gz
x86: Introduce TS_COMPAT_RESTART to fix get_nr_restart_syscall()
The comment in get_nr_restart_syscall() says: * The problem is that we can get here when ptrace pokes * syscall-like values into regs even if we're not in a syscall * at all. Yes, but if not in a syscall then the status & (TS_COMPAT|TS_I386_REGS_POKED) check below can't really help: - TS_COMPAT can't be set - TS_I386_REGS_POKED is only set if regs->orig_ax was changed by 32bit debugger; and even in this case get_nr_restart_syscall() is only correct if the tracee is 32bit too. Suppose that a 64bit debugger plays with a 32bit tracee and * Tracee calls sleep(2) // TS_COMPAT is set * User interrupts the tracee by CTRL-C after 1 sec and does "(gdb) call func()" * gdb saves the regs by PTRACE_GETREGS * does PTRACE_SETREGS to set %rip='func' and %orig_rax=-1 * PTRACE_CONT // TS_COMPAT is cleared * func() hits int3. * Debugger catches SIGTRAP. * Restore original regs by PTRACE_SETREGS. * PTRACE_CONT get_nr_restart_syscall() wrongly returns __NR_restart_syscall==219, the tracee calls ia32_sys_call_table[219] == sys_madvise. Add the sticky TS_COMPAT_RESTART flag which survives after return to user mode. It's going to be removed in the next step again by storing the information in the restart block. As a further cleanup it might be possible to remove also TS_I386_REGS_POKED with that. Test-case: $ cvs -d :pserver:anoncvs:anoncvs@sourceware.org:/cvs/systemtap co ptrace-tests $ gcc -o erestartsys-trap-debuggee ptrace-tests/tests/erestartsys-trap-debuggee.c --m32 $ gcc -o erestartsys-trap-debugger ptrace-tests/tests/erestartsys-trap-debugger.c -lutil $ ./erestartsys-trap-debugger Unexpected: retval 1, errno 22 erestartsys-trap-debugger: ptrace-tests/tests/erestartsys-trap-debugger.c:421 Fixes: 609c19a385c8 ("x86/ptrace: Stop setting TS_COMPAT in ptrace code") Reported-by: Jan Kratochvil <jan.kratochvil@redhat.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20210201174709.GA17895@redhat.com
-rw-r--r--arch/x86/include/asm/thread_info.h14
-rw-r--r--arch/x86/kernel/signal.c24
2 files changed, 14 insertions, 24 deletions
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index c2dc29e215ea..30d1d187019f 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -214,10 +214,22 @@ static inline int arch_within_stack_frames(const void * const stack,
*/
#define TS_COMPAT 0x0002 /* 32bit syscall active (64BIT)*/
+#ifndef __ASSEMBLY__
#ifdef CONFIG_COMPAT
#define TS_I386_REGS_POKED 0x0004 /* regs poked by 32-bit ptracer */
+#define TS_COMPAT_RESTART 0x0008
+
+#define arch_set_restart_data arch_set_restart_data
+
+static inline void arch_set_restart_data(struct restart_block *restart)
+{
+ struct thread_info *ti = current_thread_info();
+ if (ti->status & TS_COMPAT)
+ ti->status |= TS_COMPAT_RESTART;
+ else
+ ti->status &= ~TS_COMPAT_RESTART;
+}
#endif
-#ifndef __ASSEMBLY__
#ifdef CONFIG_X86_32
#define in_ia32_syscall() true
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index ea794a083c44..6c26d2c3a2e4 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -766,30 +766,8 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
{
- /*
- * This function is fundamentally broken as currently
- * implemented.
- *
- * The idea is that we want to trigger a call to the
- * restart_block() syscall and that we want in_ia32_syscall(),
- * in_x32_syscall(), etc. to match whatever they were in the
- * syscall being restarted. We assume that the syscall
- * instruction at (regs->ip - 2) matches whatever syscall
- * instruction we used to enter in the first place.
- *
- * The problem is that we can get here when ptrace pokes
- * syscall-like values into regs even if we're not in a syscall
- * at all.
- *
- * For now, we maintain historical behavior and guess based on
- * stored state. We could do better by saving the actual
- * syscall arch in restart_block or (with caveats on x32) by
- * checking if regs->ip points to 'int $0x80'. The current
- * behavior is incorrect if a tracer has a different bitness
- * than the tracee.
- */
#ifdef CONFIG_IA32_EMULATION
- if (current_thread_info()->status & (TS_COMPAT|TS_I386_REGS_POKED))
+ if (current_thread_info()->status & TS_COMPAT_RESTART)
return __NR_ia32_restart_syscall;
#endif
#ifdef CONFIG_X86_X32_ABI