git: 336fec57a6cc - stable/14 - linux: Fix usage of ptrace(PT_GET_SC_ARGS)

The branch stable/14 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=336fec57a6cc0a4ee58ed9a094905ad4ad7030fe

commit 336fec57a6cc0a4ee58ed9a094905ad4ad7030fe
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-06-13 19:03:03 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2025-06-30 14:19:30 +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
    
    (cherry picked from commit 48a656c588f9fb995b9c524b57dd5febd9f69168)
---
 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 a8331897316d..951d9c28b7f1 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 4d1d0ef21a15..f81013ffb842 100644
--- a/sys/kern/sys_process.c
+++ b/sys/kern/sys_process.c
@@ -696,6 +696,9 @@ 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;
@@ -1172,7 +1175,9 @@ 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
@@ -1182,11 +1187,21 @@ 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 3cce2c088f0b..85c6b2d5366a 100644
--- a/sys/sys/ptrace.h
+++ b/sys/sys/ptrace.h
@@ -89,8 +89,16 @@
 #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