From 6342adcaa683c2b705c24ed201dc11b35854c88d Mon Sep 17 00:00:00 2001 From: Gabriel Krisman Bertazi Date: Wed, 3 Feb 2021 13:00:48 -0500 Subject: 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 Signed-off-by: Gabriel Krisman Bertazi Signed-off-by: Thomas Gleixner Tested-by: Kyle Huey Link: https://lore.kernel.org/r/87h7mtc9pr.fsf_-_@collabora.com --- include/linux/entry-common.h | 1 + include/linux/thread_info.h | 2 ++ 2 files changed, 3 insertions(+) (limited to 'include') 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 -- cgit