From 32db55f26aff1d774748159a224c0ad41383c756 Mon Sep 17 00:00:00 2001
From: avg <avg@ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f>
Date: Wed, 18 Jan 2017 14:14:00 +0000
Subject: [PATCH] MFC r310630: libkvm: support access to vmm guest memory,
 allow writes to fwmem and vmm

Sponsored by:	 Panzura


git-svn-id: svn://svn.freebsd.org/base/stable/10@312382 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
---
 include/paths.h          |  1 +
 lib/libkvm/kvm.c         | 54 ++++++++++++++++++++++++++++++++++------
 lib/libkvm/kvm_private.h |  1 +
 3 files changed, 49 insertions(+), 7 deletions(-)

diff --git a/include/paths.h b/include/paths.h
index 89c9fc9cf..2ba062361 100644
--- a/include/paths.h
+++ b/include/paths.h
@@ -98,6 +98,7 @@
 #define	_PATH_VARDB	"/var/db/"
 #define	_PATH_VARRUN	"/var/run/"
 #define	_PATH_VARTMP	"/var/tmp/"
+#define	_PATH_DEVVMM	"/dev/vmm/"
 #define	_PATH_YP	"/var/yp/"
 #define	_PATH_UUCPLOCK	"/var/spool/lock/"
 
diff --git a/lib/libkvm/kvm.c b/lib/libkvm/kvm.c
index 9181a491b..85f50ad05 100644
--- a/lib/libkvm/kvm.c
+++ b/lib/libkvm/kvm.c
@@ -198,8 +198,10 @@ _kvm_open(kvm_t *kd, const char *uf, const char *mf, int flag, char *errout)
 			return (kd);
 		}
 	}
+
 	/*
-	 * This is a crash dump.
+	 * This is either a crash dump or a remote live system with its physical
+	 * memory fully accessible via a special device.
 	 * Initialize the virtual address translation machinery,
 	 * but first setup the namelist fd.
 	 */
@@ -207,8 +209,11 @@ _kvm_open(kvm_t *kd, const char *uf, const char *mf, int flag, char *errout)
 		_kvm_syserr(kd, kd->program, "%s", uf);
 		goto failed;
 	}
-	if (strncmp(mf, _PATH_FWMEM, strlen(_PATH_FWMEM)) == 0)
+	if (strncmp(mf, _PATH_FWMEM, strlen(_PATH_FWMEM)) == 0 ||
+	    strncmp(mf, _PATH_DEVVMM, strlen(_PATH_DEVVMM)) == 0) {
 		kd->rawdump = 1;
+		kd->writable = 1;
+	}
 	if (_kvm_initvtop(kd) < 0)
 		goto failed;
 	return (kd);
@@ -557,6 +562,15 @@ ssize_t
 kvm_write(kvm_t *kd, u_long kva, const void *buf, size_t len)
 {
 	int cc;
+	ssize_t cw;
+	off_t pa;
+	const char *cp;
+
+	if (!ISALIVE(kd) && !kd->writable) {
+		_kvm_err(kd, kd->program,
+		    "kvm_write not implemented for dead kernels");
+		return (-1);
+	}
 
 	if (ISALIVE(kd)) {
 		/*
@@ -574,10 +588,36 @@ kvm_write(kvm_t *kd, u_long kva, const void *buf, size_t len)
 		} else if ((size_t)cc < len)
 			_kvm_err(kd, kd->program, "short write");
 		return (cc);
-	} else {
-		_kvm_err(kd, kd->program,
-		    "kvm_write not implemented for dead kernels");
-		return (-1);
 	}
-	/* NOTREACHED */
+
+	cp = buf;
+	while (len > 0) {
+		cc = _kvm_kvatop(kd, kva, &pa);
+		if (cc == 0)
+			return (-1);
+		if (cc > (ssize_t)len)
+			cc = len;
+		errno = 0;
+		if (lseek(kd->pmfd, pa, 0) == -1 && errno != 0) {
+			_kvm_syserr(kd, 0, _PATH_MEM);
+			break;
+		}
+		cw = write(kd->pmfd, cp, cc);
+		if (cw < 0) {
+			_kvm_syserr(kd, kd->program, "kvm_write");
+			break;
+		}
+		/*
+		 * If ka_kvatop returns a bogus value or our core file is
+		 * truncated, we might wind up seeking beyond the end of the
+		 * core file in which case the read will return 0 (EOF).
+		 */
+		if (cw == 0)
+			break;
+		cp += cw;
+		kva += cw;
+		len -= cw;
+	}
+
+	return (cp - (char *)buf);
 }
diff --git a/lib/libkvm/kvm_private.h b/lib/libkvm/kvm_private.h
index b3eeea7ad..c47eb079a 100644
--- a/lib/libkvm/kvm_private.h
+++ b/lib/libkvm/kvm_private.h
@@ -62,6 +62,7 @@ struct __kvm {
 	 */
 	struct vmstate *vmst;
 	int	rawdump;	/* raw dump format */
+	int	writable;	/* physical memory is writable */
 
 	int		vnet_initialized;	/* vnet fields set up */
 	uintptr_t	vnet_start;	/* start of kernel's vnet region */
-- 
2.45.0