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entry: Ensure trap after single-step on system call return
Commit2991552447
("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
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@ -43,8 +43,6 @@ static __always_inline void arch_check_user_regs(struct pt_regs *regs)
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}
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}
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#define arch_check_user_regs arch_check_user_regs
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#define arch_check_user_regs arch_check_user_regs
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#define ARCH_SYSCALL_EXIT_WORK (_TIF_SINGLESTEP)
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static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
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static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
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unsigned long ti_work)
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unsigned long ti_work)
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{
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{
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@ -127,12 +127,17 @@ static int enable_single_step(struct task_struct *child)
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regs->flags |= X86_EFLAGS_TF;
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regs->flags |= X86_EFLAGS_TF;
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/*
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/*
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* Always set TIF_SINGLESTEP - this guarantees that
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* Always set TIF_SINGLESTEP. This will also
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* we single-step system calls etc.. This will also
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* cause us to set TF when returning to user mode.
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* cause us to set TF when returning to user mode.
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*/
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*/
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set_tsk_thread_flag(child, TIF_SINGLESTEP);
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set_tsk_thread_flag(child, TIF_SINGLESTEP);
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/*
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* Ensure that a trap is triggered once stepping out of a system
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* call prior to executing any user instruction.
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*/
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set_task_syscall_work(child, SYSCALL_EXIT_TRAP);
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oflags = regs->flags;
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oflags = regs->flags;
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/* Set TF on the kernel stack.. */
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/* Set TF on the kernel stack.. */
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@ -230,6 +235,7 @@ void user_disable_single_step(struct task_struct *child)
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/* Always clear TIF_SINGLESTEP... */
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/* Always clear TIF_SINGLESTEP... */
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clear_tsk_thread_flag(child, TIF_SINGLESTEP);
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clear_tsk_thread_flag(child, TIF_SINGLESTEP);
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clear_task_syscall_work(child, SYSCALL_EXIT_TRAP);
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/* But touch TF only if it was set by us.. */
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/* But touch TF only if it was set by us.. */
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if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
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if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
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@ -46,6 +46,7 @@
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SYSCALL_WORK_SYSCALL_TRACE | \
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SYSCALL_WORK_SYSCALL_TRACE | \
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SYSCALL_WORK_SYSCALL_AUDIT | \
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SYSCALL_WORK_SYSCALL_AUDIT | \
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SYSCALL_WORK_SYSCALL_USER_DISPATCH | \
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SYSCALL_WORK_SYSCALL_USER_DISPATCH | \
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SYSCALL_WORK_SYSCALL_EXIT_TRAP | \
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ARCH_SYSCALL_WORK_EXIT)
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ARCH_SYSCALL_WORK_EXIT)
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/*
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/*
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@ -43,6 +43,7 @@ enum syscall_work_bit {
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SYSCALL_WORK_BIT_SYSCALL_EMU,
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SYSCALL_WORK_BIT_SYSCALL_EMU,
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SYSCALL_WORK_BIT_SYSCALL_AUDIT,
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SYSCALL_WORK_BIT_SYSCALL_AUDIT,
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SYSCALL_WORK_BIT_SYSCALL_USER_DISPATCH,
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SYSCALL_WORK_BIT_SYSCALL_USER_DISPATCH,
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SYSCALL_WORK_BIT_SYSCALL_EXIT_TRAP,
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};
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};
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#define SYSCALL_WORK_SECCOMP BIT(SYSCALL_WORK_BIT_SECCOMP)
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#define SYSCALL_WORK_SECCOMP BIT(SYSCALL_WORK_BIT_SECCOMP)
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@ -51,6 +52,7 @@ enum syscall_work_bit {
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#define SYSCALL_WORK_SYSCALL_EMU BIT(SYSCALL_WORK_BIT_SYSCALL_EMU)
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#define SYSCALL_WORK_SYSCALL_EMU BIT(SYSCALL_WORK_BIT_SYSCALL_EMU)
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#define SYSCALL_WORK_SYSCALL_AUDIT BIT(SYSCALL_WORK_BIT_SYSCALL_AUDIT)
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#define SYSCALL_WORK_SYSCALL_AUDIT BIT(SYSCALL_WORK_BIT_SYSCALL_AUDIT)
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#define SYSCALL_WORK_SYSCALL_USER_DISPATCH BIT(SYSCALL_WORK_BIT_SYSCALL_USER_DISPATCH)
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#define SYSCALL_WORK_SYSCALL_USER_DISPATCH BIT(SYSCALL_WORK_BIT_SYSCALL_USER_DISPATCH)
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#define SYSCALL_WORK_SYSCALL_EXIT_TRAP BIT(SYSCALL_WORK_BIT_SYSCALL_EXIT_TRAP)
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#endif
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#endif
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#include <asm/thread_info.h>
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#include <asm/thread_info.h>
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@ -209,15 +209,9 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
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lockdep_sys_exit();
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lockdep_sys_exit();
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}
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}
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#ifndef _TIF_SINGLESTEP
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static inline bool report_single_step(unsigned long work)
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{
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return false;
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}
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#else
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/*
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/*
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* If SYSCALL_EMU is set, then the only reason to report is when
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* If SYSCALL_EMU is set, then the only reason to report is when
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* TIF_SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall
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* SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP). This syscall
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* instruction has been already reported in syscall_enter_from_user_mode().
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* instruction has been already reported in syscall_enter_from_user_mode().
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*/
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*/
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static inline bool report_single_step(unsigned long work)
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static inline bool report_single_step(unsigned long work)
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@ -225,10 +219,8 @@ static inline bool report_single_step(unsigned long work)
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if (work & SYSCALL_WORK_SYSCALL_EMU)
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if (work & SYSCALL_WORK_SYSCALL_EMU)
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return false;
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return false;
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return !!(current_thread_info()->flags & _TIF_SINGLESTEP);
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return work & SYSCALL_WORK_SYSCALL_EXIT_TRAP;
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}
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}
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#endif
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static void syscall_exit_work(struct pt_regs *regs, unsigned long work)
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static void syscall_exit_work(struct pt_regs *regs, unsigned long work)
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{
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{
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