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| author | Gabriel Krisman Bertazi <krisman@collabora.com> | 2021-02-03 19:00:48 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2021-02-06 00:21:42 +0100 |
| commit | 6342adcaa683c2b705c24ed201dc11b35854c88d (patch) | |
| tree | d75d12186c1d9e79168bdd0b84740d7701bee408 /kernel/entry | |
| parent | Linux 5.11-rc6 (diff) | |
| download | linux-6342adcaa683c2b705c24ed201dc11b35854c88d.tar.xz linux-6342adcaa683c2b705c24ed201dc11b35854c88d.zip | |
entry: Ensure trap after single-step on system call return
Commit 299155244770 ("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: 299155244770 ("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
Diffstat (limited to 'kernel/entry')
| -rw-r--r-- | kernel/entry/common.c | 12 |
1 files changed, 2 insertions, 10 deletions
diff --git a/kernel/entry/common.c b/kernel/entry/common.c index 6dd82be60df8..f9d491b17b78 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -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) { |