tmakin/ack-tegra
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

entry: Ensure trap after single-step on system call return

Browse Source 
Commit 2991552447 ("entry: Drop usage of TIF flags in the generic syscall
code") introduced a bug on architectures using the generic syscall entry
code, in which processes stopped by PTRACE_SYSCALL do not trap on syscall
return after receiving a TIF_SINGLESTEP.

The reason is that the meaning of TIF_SINGLESTEP flag is overloaded to
cause the trap after a system call is executed, but since the above commit,
the syscall call handler only checks for the SYSCALL_WORK flags on the exit
work.

Split the meaning of TIF_SINGLESTEP such that it only means single-step
mode, and create a new type of SYSCALL_WORK to request a trap immediately
after a syscall in single-step mode.  In the current implementation, the
SYSCALL_WORK flag shadows the TIF_SINGLESTEP flag for simplicity.

Update x86 to flip this bit when a tracer enables single stepping.

Fixes: 2991552447 ("entry: Drop usage of TIF flags in the generic syscall code")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Kyle Huey <me@kylehuey.com>
Link: https://lore.kernel.org/r/87h7mtc9pr.fsf_-_@collabora.com
This commit is contained in:
Gabriel Krisman Bertazi
2021-02-03 13:00:48 -05:00
committed by Thomas Gleixner
parent 1048ba83fb
commit 6342adcaa6
5 changed files with 13 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files
kernel/entry/common.c
+2 -10
View File
@@ -209,15 +209,9 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
lockdep_sys_exit();
}
#ifndef _TIF_SINGLESTEP
static inline bool report_single_step(unsigned long work)
{
return false;
}
#else
/*
* If SYSCALL_EMU is set, then the only reason to report is when
* TIF_SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall
* SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall
* instruction has been already reported in syscall_enter_from_user_mode().
*/
static inline bool report_single_step(unsigned long work)
@@ -225,10 +219,8 @@ static inline bool report_single_step(unsigned long work)
if (work & SYSCALL_WORK_SYSCALL_EMU)
return false;
return !!(current_thread_info()->flags & _TIF_SINGLESTEP);
return work & SYSCALL_WORK_SYSCALL_EXIT_TRAP;
}
#endif
static void syscall_exit_work(struct pt_regs *regs, unsigned long work)
{