Date: Fri, 20 Jan 2023 03:23:47 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: efde0099aacd - stable/13 - ptrace(2): document PT_SC_REMOTE Message-ID: <202301200323.30K3NlNE042643@gitrepo.freebsd.org>
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The branch stable/13 has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=efde0099aacdb14bfcb8eb77498ccf2800219b78 commit efde0099aacdb14bfcb8eb77498ccf2800219b78 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2022-12-02 03:00:08 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2023-01-20 03:21:11 +0000 ptrace(2): document PT_SC_REMOTE Tested by: pho (cherry picked from commit a98613f2389227effeb9d86e47e53ea01ecddfe5) --- lib/libc/sys/ptrace.2 | 73 +++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 68 insertions(+), 5 deletions(-) diff --git a/lib/libc/sys/ptrace.2 b/lib/libc/sys/ptrace.2 index b107dcef97ae..a5e67c745422 100644 --- a/lib/libc/sys/ptrace.2 +++ b/lib/libc/sys/ptrace.2 @@ -976,10 +976,44 @@ The size of .Vt "struct ptrace_coredump" must be passed in .Fa data . -.Pp -The process must be stopped before dumping core. +.It Dv PT_SC_REMOTE +Request to execute a syscall in the context of the traced process, +in the specified thread. +The +.Fa addr +argument must point to the +.Vt "struct ptrace_sc_remote" , +which describes the requested syscall and its arguments, and receives +the result. +The size of +.Vt "struct ptrace_sc_remote" +must be passed in +.Fa data. +.Bd -literal +struct ptrace_sc_remote { + struct ptrace_sc_ret pscr_ret; + u_int pscr_syscall; + u_int pscr_nargs; + u_long *pscr_args; +}; +.Ed +The +.Dv pscr_syscall +contains the syscall number to execute, the +.Dv pscr_nargs +is the number of supplied arguments, which are supplied in the +.Dv pscr_args +array. +Result of the execution is returned in the +.Dv pscr_ret +member. +Note that the request and its result do not affect the returned value from +the currently executed syscall, if any. +.El +.Sh PT_COREDUMP and PT_SC_REMOTE usage +The process must be stopped before dumping or initiating a remote system call. A single thread in the target process is temporarily unsuspended -in kernel to write the dump. +in the kernel to perform the action. If the .Nm call fails before a thread is unsuspended, there is no event to @@ -996,9 +1030,38 @@ an error occurred, it is recommended to unconditionally perform with .Dv WNOHANG flag after -.Dv PT_COREDUMP , +.Dv PT_COREDUMP +and +.Dv PT_SC_REMOTE , and silently accept zero result from it. -.El +.Pp +For +.Dv PT_SC_REMOTE , +the selected thread must be stopped in the safe place, which is +currently defined as a syscall exit, or a return from kernel to +user mode (basically, a signal handler call place). +Kernel returns +.Er EBUSY +status if attempt is made to execute remote syscall at unsafe stop. +.Pp +Note that neither +.Dv kern.trap_enotcap +sysctl setting, nor the corresponding +.Xr procctl 2 +flag +.Dv PROC_TRAPCAP_CTL_ENABLE +are obeyed during the execution of the syscall by +.Dv PT_SC_REMOTE . +In other words, +.Dv SIGTRAP +signal is not sent to a process executing in capability mode, +which violated a mode access restriction. +.Pp +Note that due to the mode of execution for the remote syscall, in +particular, the setting where only one thread is allowed to run, +the syscall might block on resources owned by suspended threads. +This might result in the target process deadlock. +In this situation, the only way out is to kill the target. .Sh ARM MACHINE-SPECIFIC REQUESTS .Bl -tag -width "Dv PT_SETVFPREGS" .It Dv PT_GETVFPREGS
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