Add ptrace commands used to read/write the XSAVE area of a traced

process. Intended to give debuggers access to xmm/ymm registers.

Inspired by FreeBSD which exposes a similar set of ptrace commands.

ok kettenis@

lib/libc/sys/ptrace.2

@@ -1,8 +1,8 @@
-.\"	$OpenBSD: ptrace.2,v 1.43 2022/09/11 06:38:11 jmc Exp $
+.\"	$OpenBSD: ptrace.2,v 1.44 2024/11/27 05:25:56 anton Exp $
 .\"	$NetBSD: ptrace.2,v 1.3 1996/02/23 01:39:41 jtc Exp $
 .\"
 .\" This file is in the public domain.
-.Dd $Mdocdate: September 11 2022 $
+.Dd $Mdocdate: November 27 2024 $
 .Dt PTRACE 2
 .Os
 .Sh NAME
@@ -500,6 +500,58 @@ pointed to by
 The window cookie needs to be
 .Sq XOR'ed
 to stack-saved program counters.
+.It Dv PT_GETXSTATE_INFO Pq amd64 only
+This request can be used to obtain details about the traced process XSAVE area,
+specified in a
+.Dq Li "struct ptrace_xstate_info"
+defined as follows:
+.Bd -literal -offset indent
+struct ptrace_xstate_info {
+	uint64_t xsave_mask;
+	uint32_t xsave_len;
+};
+.Ed
+.Pp
+The
+.Fa xsave_mask
+field denotes the enabled XSAVE components.
+The
+.Fa xsave_len
+field denotes the size of XSAVE area intended to be used with the
+.Dv PT_GETXSTATE
+and
+.Dv PT_SETXSTATE
+requests.
+.Pp
+A pointer to
+.Dq Li "struct ptrace_xstate_info"
+must be passed in
+.Fa addr
+and the
+.Fa data
+argument must be set to
+.Li sizeof(struct ptrace_xstate_info) .
+.It Dv PT_GETXSTATE Pq amd64 only
+This request can be used to read the XSAVE area of the traced process.
+A pointer to a buffer must be passed in
+.Fa addr
+with a capacity of the length obtained using the
+.Dv PT_GETXSTATE_INFO
+request.
+The
+.Fa data
+argument must reflect the same length.
+.It Dv PT_SETXSTATE Pq amd64 only
+This request can be used to write the XSAVE area of the traced process.
+Only changes to the x87, SSE and AVX state components are honored.
+A pointer to a buffer must be passed in
+.Fa addr
+with a capacity of the length obtained using the
+.Dv PT_GETXSTATE_INFO
+request.
+The
+.Fa data
+argument must reflect the same length.
 .El
 .Sh ERRORS
 Some requests can cause
@@ -579,6 +631,12 @@ An attempt was made to use
 .Dv PT_ATTACH
 on a system process.
 .El
+.It Bq Er ENOTSUP
+.Dv PT_GETXSTATE_INFO ,
+.Dv PT_GETXSTATE ,
+or
+.Dv PT_SETXSTATE
+was attempted on a CPU lacking support for XSAVE.
 .El
 .Sh HISTORY
 The

sys/arch/amd64/amd64/process_machdep.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: process_machdep.c,v 1.17 2024/05/13 01:15:50 jsg Exp $	*/
+/*	$OpenBSD: process_machdep.c,v 1.18 2024/11/27 05:25:56 anton Exp $	*/
 /*	$NetBSD: process_machdep.c,v 1.1 2003/04/26 18:39:31 fvdl Exp $	*/
 
 /*-
@@ -56,6 +56,7 @@
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/proc.h>
+#include <sys/ptrace.h>
 #include <sys/user.h>
 
 #include <uvm/uvm_extern.h>
@@ -200,4 +201,84 @@ process_set_pc(struct proc *p, caddr_t addr)
 	return (0);
 }
 
+int
+process_read_xstate_info(struct proc *p, void *addr)
+{
+	struct ptrace_xstate_info *info = addr;
+
+	if (xsave_mask == 0)
+		return (ENOTSUP);
+
+	info->xsave_mask = xsave_mask;
+	info->xsave_len = fpu_save_len;
+	return (0);
+}
+
+struct xsave_area {
+	uint8_t	legacy_region[512];
+
+	struct xsave_header {
+		uint64_t	xstate_bv;
+		uint64_t	xcomp_bv;
+		uint8_t		rsvd0[48];
+	} xsave_header;
+
+	uint8_t	extended_region[];
+} __attribute__((packed));
+
+#define XSTATE_COMPONENT_X87	(1ULL << 0)
+#define XSTATE_COMPONENT_SSE	(1ULL << 1)
+#define XSTATE_COMPONENT_AVX	(1ULL << 2)
+
+int
+process_read_xstate(struct proc *p, void *addr)
+{
+	struct xsave_area *area =
+	    (struct xsave_area *)&p->p_addr->u_pcb.pcb_savefpu;
+
+	if (xsave_mask == 0)
+		return (ENOTSUP);
+
+	memcpy(addr, area, fpu_save_len);
+	return (0);
+}
+
+int
+process_write_xstate(struct proc *p, void *addr)
+{
+	struct xsave_area *area =
+	    (struct xsave_area *)&p->p_addr->u_pcb.pcb_savefpu;
+	struct xsave_area *new_area = (struct xsave_area *)addr;
+	uint32_t offset_extended_region = offsetof(struct xsave_area,
+	    extended_region);
+	uint32_t a, b, c, d;
+
+	if (xsave_mask == 0)
+		return (ENOTSUP);
+
+	/*
+	 * Honor changes to x87, SSE and AVX components and mark them as in use.
+	 * Required to ensure any changes are restored once the traced process
+	 * continues execution.
+	 */
+	if ((xsave_mask & XSTATE_COMPONENT_X87) ||
+	    (xsave_mask & XSTATE_COMPONENT_SSE)) {
+		memcpy(area->legacy_region, new_area->legacy_region,
+		    sizeof(area->legacy_region));
+		area->xsave_header.xstate_bv |= xsave_mask &
+		    (XSTATE_COMPONENT_X87 | XSTATE_COMPONENT_SSE);
+	}
+	if (xsave_mask & XSTATE_COMPONENT_AVX) {
+		CPUID_LEAF(0xd, 2, a, b, c, d);
+		if (offset_extended_region == b &&
+		    offset_extended_region + a <= fpu_save_len) {
+			memcpy(area->extended_region,
+			    new_area->extended_region, a);
+			area->xsave_header.xstate_bv |= XSTATE_COMPONENT_AVX;
+		}
+	}
+
+	return (0);
+}
+
 #endif	/* PTRACE */

sys/arch/amd64/include/ptrace.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ptrace.h,v 1.1 2004/01/28 01:39:39 mickey Exp $	*/
+/*	$OpenBSD: ptrace.h,v 1.2 2024/11/27 05:25:57 anton Exp $	*/
 /*	$NetBSD: ptrace.h,v 1.1 2003/04/26 18:39:47 fvdl Exp $	*/
 
 /*
@@ -39,3 +39,18 @@
 #define	PT_SETREGS	(PT_FIRSTMACH + 2)
 #define	PT_GETFPREGS	(PT_FIRSTMACH + 3)
 #define	PT_SETFPREGS	(PT_FIRSTMACH + 4)
+
+#define	PT_GETXSTATE_INFO	(PT_FIRSTMACH + 5)
+#define	PT_GETXSTATE		(PT_FIRSTMACH + 6)
+#define	PT_SETXSTATE		(PT_FIRSTMACH + 7)
+
+struct ptrace_xstate_info {
+	uint64_t	xsave_mask;
+	uint32_t	xsave_len;
+};
+
+#ifdef _KERNEL
+int	process_read_xstate_info(struct proc *, void *);
+int	process_read_xstate(struct proc *, void *);
+int	process_write_xstate(struct proc *, void *);
+#endif

sys/kern/sys_process.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: sys_process.c,v 1.102 2024/10/08 12:02:24 claudio Exp $	*/
+/*	$OpenBSD: sys_process.c,v 1.103 2024/11/27 05:25:57 anton Exp $	*/
 /*	$NetBSD: sys_process.c,v 1.55 1996/05/15 06:17:47 tls Exp $	*/
 
 /*-
@@ -66,6 +66,7 @@
 
 #include <uvm/uvm_extern.h>
 
+#include <machine/fpu.h>
 #include <machine/reg.h>
 
 #ifdef PTRACE
@@ -206,6 +207,24 @@ sys_ptrace(struct proc *p, void *v, register_t *retval)
 		mode = OUT;
 		size = sizeof u.u_pacmask;
 		break;
+#endif
+#ifdef PT_GETXSTATE_INFO
+	case PT_GETXSTATE_INFO:
+		mode = OUT_ALLOC;
+		size = sizeof(struct ptrace_xstate_info);
+		break;
+#endif
+#ifdef PT_GETXSTATE
+	case PT_GETXSTATE:
+		mode = OUT_ALLOC;
+		size = fpu_save_len;
+		break;
+#endif
+#ifdef PT_SETXSTATE
+	case PT_SETXSTATE:
+		mode = IN_ALLOC;
+		size = fpu_save_len;
+		break;
 #endif
 	default:
 		return EINVAL;
@@ -759,6 +778,18 @@ ptrace_ustate(struct proc *p, int req, pid_t pid, void *addr, int data,
 		((register_t *)addr)[0] = process_get_pacmask(t);
 		((register_t *)addr)[1] = process_get_pacmask(t);
 		return 0;
+#endif
+#ifdef PT_GETXSTATE_INFO
+	case PT_GETXSTATE_INFO:
+		return process_read_xstate_info(t, addr);
+#endif
+#ifdef PT_GETXSTATE
+	case PT_GETXSTATE:
+		return process_read_xstate(t, addr);
+#endif
+#ifdef PT_SETXSTATE
+	case PT_SETXSTATE:
+		return process_write_xstate(t, addr);
 #endif
 	default:
 		KASSERTMSG(0, "%s: unhandled request %d", __func__, req);