Date: Fri, 13 Jun 2025 19:20:14 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 48a656c588f9 - main - linux: Fix usage of ptrace(PT_GET_SC_ARGS) Message-ID: <202506131920.55DJKEGT006179@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=48a656c588f9fb995b9c524b57dd5febd9f69168 commit 48a656c588f9fb995b9c524b57dd5febd9f69168 Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2025-06-13 19:03:03 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2025-06-13 19:19:59 +0000 linux: Fix usage of ptrace(PT_GET_SC_ARGS) The native handler expects the argument to be a pointer to an array of 8 syscall arguments, whereas the emulation provided an array that holds up to 6. Handle this by adding a new range of Linuxulator-specific ptrace commands. In particular, introduce PTLINUX_GET_SC_ARGS, which always copies exactly six arguments. This fixes the problem and removes the hack of checking the target thread ABI to decide whether to apply a Linux-specific quirk to PT_GET_SC_ARGS. Reviewed by: kib MFC after: 2 weeks Sponsored by: Klara, Inc. Differential Revision: https://reviews.freebsd.org/D50758 --- sys/compat/freebsd32/freebsd32_misc.c | 3 +++ sys/compat/linux/linux_ptrace.c | 18 ++++-------------- sys/kern/sys_process.c | 27 +++++++++++++++++++++------ sys/sys/ptrace.h | 8 ++++++++ 4 files changed, 36 insertions(+), 20 deletions(-) diff --git a/sys/compat/freebsd32/freebsd32_misc.c b/sys/compat/freebsd32/freebsd32_misc.c index cc777f2bf830..75fdb1f544ca 100644 --- a/sys/compat/freebsd32/freebsd32_misc.c +++ b/sys/compat/freebsd32/freebsd32_misc.c @@ -1177,6 +1177,9 @@ freebsd32_ptrace(struct thread *td, struct freebsd32_ptrace_args *uap) pscr_args[i] = pscr_args32[i]; r.sr.pscr_args = pscr_args; break; + case PTLINUX_FIRST ... PTLINUX_LAST: + error = EINVAL; + break; default: addr = uap->addr; break; diff --git a/sys/compat/linux/linux_ptrace.c b/sys/compat/linux/linux_ptrace.c index 421760eab2a9..0dbfd2177122 100644 --- a/sys/compat/linux/linux_ptrace.c +++ b/sys/compat/linux/linux_ptrace.c @@ -386,21 +386,11 @@ linux_ptrace_get_syscall_info(struct thread *td, pid_t pid, if (lwpinfo.pl_flags & PL_FLAG_SCE) { si.op = LINUX_PTRACE_SYSCALL_INFO_ENTRY; si.entry.nr = lwpinfo.pl_syscall_code; - /* - * The use of PT_GET_SC_ARGS there is special, - * implementation of PT_GET_SC_ARGS for Linux-ABI - * callers emulates Linux bug which strace(1) depends - * on: at initialization it tests whether ptrace works - * by calling close(2), or some other single-argument - * syscall, _with six arguments_, and then verifies - * whether it can fetch them all using this API; - * otherwise it bails out. - */ - error = kern_ptrace(td, PT_GET_SC_ARGS, pid, - &si.entry.args, sizeof(si.entry.args)); + error = kern_ptrace(td, PTLINUX_GET_SC_ARGS, pid, + si.entry.args, sizeof(si.entry.args)); if (error != 0) { - linux_msg(td, "PT_GET_SC_ARGS failed with error %d", - error); + linux_msg(td, + "PT_LINUX_GET_SC_ARGS failed with error %d", error); return (error); } } else if (lwpinfo.pl_flags & PL_FLAG_SCX) { diff --git a/sys/kern/sys_process.c b/sys/kern/sys_process.c index 8b382cb3048e..821c537065b3 100644 --- a/sys/kern/sys_process.c +++ b/sys/kern/sys_process.c @@ -690,6 +690,9 @@ sys_ptrace(struct thread *td, struct ptrace_args *uap) break; r.sr.pscr_args = pscr_args; break; + case PTLINUX_FIRST ... PTLINUX_LAST: + error = EINVAL; + break; default: addr = uap->addr; break; @@ -1166,7 +1169,9 @@ kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data) break; case PT_GET_SC_ARGS: - CTR1(KTR_PTRACE, "PT_GET_SC_ARGS: pid %d", p->p_pid); + case PTLINUX_GET_SC_ARGS: + CTR2(KTR_PTRACE, "%s: pid %d", req == PT_GET_SC_ARGS ? + "PT_GET_SC_ARGS" : "PT_LINUX_GET_SC_ARGS", p->p_pid); if (((td2->td_dbgflags & (TDB_SCE | TDB_SCX)) == 0 && td2->td_sa.code == 0) #ifdef COMPAT_FREEBSD32 @@ -1176,11 +1181,21 @@ kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data) error = EINVAL; break; } - bzero(addr, sizeof(td2->td_sa.args)); - /* See the explanation in linux_ptrace_get_syscall_info(). */ - bcopy(td2->td_sa.args, addr, SV_PROC_ABI(td->td_proc) == - SV_ABI_LINUX ? sizeof(td2->td_sa.args) : - td2->td_sa.callp->sy_narg * sizeof(syscallarg_t)); + if (req == PT_GET_SC_ARGS) { + bzero(addr, sizeof(td2->td_sa.args)); + bcopy(td2->td_sa.args, addr, td2->td_sa.callp->sy_narg * + sizeof(syscallarg_t)); + } else { + /* + * Emulate a Linux bug which which strace(1) depends on: + * at initialization it tests whether ptrace works by + * calling close(2), or some other single-argument + * syscall, _with six arguments_, and then verifies + * whether it can fetch them all using this API; + * otherwise it bails out. + */ + bcopy(td2->td_sa.args, addr, 6 * sizeof(syscallarg_t)); + } break; case PT_GET_SC_RET: diff --git a/sys/sys/ptrace.h b/sys/sys/ptrace.h index 3a7b87bfc85f..13291cd31cf5 100644 --- a/sys/sys/ptrace.h +++ b/sys/sys/ptrace.h @@ -87,8 +87,16 @@ #define PT_SC_REMOTE 44 /* Execute a syscall */ #define PT_FIRSTMACH 64 /* for machine-specific requests */ +#define PT_LASTMACH 127 #include <machine/ptrace.h> /* machine-specific requests, if any */ +#ifdef _KERNEL +/* Space for Linux ptrace emulation. */ +#define PTLINUX_FIRST 128 +#define PTLINUX_LAST 191 +#define PTLINUX_GET_SC_ARGS (PTLINUX_FIRST + 0) +#endif + /* Events used with PT_GET_EVENT_MASK and PT_SET_EVENT_MASK */ #define PTRACE_EXEC 0x0001 #define PTRACE_SCE 0x0002
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