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authorGabriel Krisman Bertazi <krisman@collabora.com>2021-02-03 21:00:48 +0300
committerThomas Gleixner <tglx@linutronix.de>2021-02-06 02:21:42 +0300
commit6342adcaa683c2b705c24ed201dc11b35854c88d (patch)
treed75d12186c1d9e79168bdd0b84740d7701bee408
parent1048ba83fb1c00cd24172e23e8263972f6b5d9ac (diff)
downloadlinux-6342adcaa683c2b705c24ed201dc11b35854c88d.tar.xz
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
-rw-r--r--arch/x86/include/asm/entry-common.h2
-rw-r--r--arch/x86/kernel/step.c10
-rw-r--r--include/linux/entry-common.h1
-rw-r--r--include/linux/thread_info.h2
-rw-r--r--kernel/entry/common.c12
5 files changed, 13 insertions, 14 deletions
diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 6fe54b2813c1..2b87b191b3b8 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -43,8 +43,6 @@ static __always_inline void arch_check_user_regs(struct pt_regs *regs)
}
#define arch_check_user_regs arch_check_user_regs
-#define ARCH_SYSCALL_EXIT_WORK (_TIF_SINGLESTEP)
-
static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
unsigned long ti_work)
{
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 60d2c3798ba2..0f3c307b37b3 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -127,12 +127,17 @@ static int enable_single_step(struct task_struct *child)
regs->flags |= X86_EFLAGS_TF;
/*
- * Always set TIF_SINGLESTEP - this guarantees that
- * we single-step system calls etc.. This will also
+ * Always set TIF_SINGLESTEP. This will also
* cause us to set TF when returning to user mode.
*/
set_tsk_thread_flag(child, TIF_SINGLESTEP);
+ /*
+ * Ensure that a trap is triggered once stepping out of a system
+ * call prior to executing any user instruction.
+ */
+ set_task_syscall_work(child, SYSCALL_EXIT_TRAP);
+
oflags = regs->flags;
/* Set TF on the kernel stack.. */
@@ -230,6 +235,7 @@ void user_disable_single_step(struct task_struct *child)
/* Always clear TIF_SINGLESTEP... */
clear_tsk_thread_flag(child, TIF_SINGLESTEP);
+ clear_task_syscall_work(child, SYSCALL_EXIT_TRAP);
/* But touch TF only if it was set by us.. */
if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index ca86a00abe86..a104b298019a 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -46,6 +46,7 @@
SYSCALL_WORK_SYSCALL_TRACE | \
SYSCALL_WORK_SYSCALL_AUDIT | \
SYSCALL_WORK_SYSCALL_USER_DISPATCH | \
+ SYSCALL_WORK_SYSCALL_EXIT_TRAP | \
ARCH_SYSCALL_WORK_EXIT)
/*
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index c8a974cead73..9b2158c69275 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -43,6 +43,7 @@ enum syscall_work_bit {
SYSCALL_WORK_BIT_SYSCALL_EMU,
SYSCALL_WORK_BIT_SYSCALL_AUDIT,
SYSCALL_WORK_BIT_SYSCALL_USER_DISPATCH,
+ SYSCALL_WORK_BIT_SYSCALL_EXIT_TRAP,
};
#define SYSCALL_WORK_SECCOMP BIT(SYSCALL_WORK_BIT_SECCOMP)
@@ -51,6 +52,7 @@ enum syscall_work_bit {
#define SYSCALL_WORK_SYSCALL_EMU BIT(SYSCALL_WORK_BIT_SYSCALL_EMU)
#define SYSCALL_WORK_SYSCALL_AUDIT BIT(SYSCALL_WORK_BIT_SYSCALL_AUDIT)
#define SYSCALL_WORK_SYSCALL_USER_DISPATCH BIT(SYSCALL_WORK_BIT_SYSCALL_USER_DISPATCH)
+#define SYSCALL_WORK_SYSCALL_EXIT_TRAP BIT(SYSCALL_WORK_BIT_SYSCALL_EXIT_TRAP)
#endif
#include <asm/thread_info.h>
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)
{