[PATCH v9 2/3] Introduce upoken function and expose it to LuaJIT scripts

Victor Krapivensky krapivenskiy.va at phystech.edu
Tue Jul 25 12:59:52 UTC 2017


This patch implies that we have process_vm_writev if and only if we have
process_vm_readv, and that they are either both supported or both
unsupported.

* defs.h: Add declaration for upoken.
* luajit.h (func_upoke): New wrapper function.
(init_luajit): Expose it as strace.upoke.
* luajit_lib.lua (write_obj): New function.
* strace.1 (LUAJIT SCRIPTING): Describe changes.
* util.c (strace_process_vm_writev): New function.
(vm_write_mem): Likewise.
(partial_poke): Likewise.
(upoken): Likewise.
---
 defs.h         |   3 +
 luajit.h       |   8 +++
 luajit_lib.lua |  10 ++++
 strace.1       |   6 ++
 util.c         | 172 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 199 insertions(+)

diff --git a/defs.h b/defs.h
index 0de6cacc..900220f1 100644
--- a/defs.h
+++ b/defs.h
@@ -441,6 +441,9 @@ umoven_or_printaddr_ignore_syserror(struct tcb *, kernel_ulong_t addr,
 extern int
 umovestr(struct tcb *, kernel_ulong_t addr, unsigned int len, char *laddr);
 
+extern int
+upoken(struct tcb *, kernel_ulong_t addr, unsigned int len, const void *laddr);
+
 extern int upeek(int pid, unsigned long, kernel_ulong_t *);
 extern int upoke(int pid, unsigned long, kernel_ulong_t);
 
diff --git a/luajit.h b/luajit.h
index 154caf6c..c486e752 100644
--- a/luajit.h
+++ b/luajit.h
@@ -149,6 +149,12 @@ func_umove_str(kernel_ulong_t addr, size_t len, char *laddr)
 	return current_tcp ? umovestr(current_tcp, addr, len, laddr) : -1;
 }
 
+static int
+func_upoke(kernel_ulong_t addr, size_t len, const void *laddr)
+{
+	return current_tcp ? upoken(current_tcp, addr, len, laddr) : -1;
+}
+
 static bool
 func_path_match_arr(const char **set, size_t nset)
 {
@@ -264,6 +270,8 @@ init_luajit(const char *scriptfile)
 		kernel_ulong_t, size_t, void *);
 	EXPOSE_FUNC(int, func_umove_str, "umove_str",
 		kernel_ulong_t, size_t, char *);
+	EXPOSE_FUNC(int, func_upoke, "upoke",
+		kernel_ulong_t, size_t, const void *);
 	EXPOSE_FUNC(bool, func_path_match_arr, "path_match_arr",
 		const char **, size_t);
 
diff --git a/luajit_lib.lua b/luajit_lib.lua
index 9b303d96..2f80ef3b 100644
--- a/luajit_lib.lua
+++ b/luajit_lib.lua
@@ -235,6 +235,16 @@ function strace.read_path(addr)
 	return strace.read_str(addr, strace.path_max, strace.path_max + 1)
 end
 
+function strace.write_obj(addr, obj)
+	local n = ffi.sizeof(obj)
+	-- work around FFI pointer semantics
+	if n == ptr_size then
+		-- it may be a pointer, and it is cheap to create a local copy
+		obj = ffi.typeof('$ [1]', ffi.typeof(obj))(obj)
+	end
+	assert(strace.upoke(addr, n, obj) == 0, 'cannot write')
+end
+
 local function parse_when(when)
 	if type(when) == 'table' then
 		return unpack(when)
diff --git a/strace.1 b/strace.1
index 798dffcd..56cf7737 100644
--- a/strace.1
+++ b/strace.1
@@ -1063,6 +1063,12 @@ Reads a path C string from the current tracee process at address \fIaddr\fR.
 Returns a Lua string on success, \fBnil, "readerr"\fR on read error, and
 \fBnil, "toolong"\fR if the \fBPATH_MAX\fR limit was exceeded.
 .TP
+\fBstrace.write_obj\fR(\fIaddr\fR, \fIobj\fR)
+Writes a FFI cdata object \fIobj\fR to the current tracee process' address space
+at address \fIaddr\fR.
+.IP
+Raises an error on failure.
+.TP
 \fBstrace.monitor_name\fR(\fIscname\fR, \fIwhen\fR)
 Marks syscall with name \fIscname\fR as to be returned from
 \fBstrace.next_sc()\fR.
diff --git a/util.c b/util.c
index 06a939e7..e2250c05 100644
--- a/util.c
+++ b/util.c
@@ -962,6 +962,20 @@ static ssize_t strace_process_vm_readv(pid_t pid,
 	return syscall(__NR_process_vm_readv, (long)pid, lvec, liovcnt, rvec, riovcnt, flags);
 }
 # define process_vm_readv strace_process_vm_readv
+
+/*
+ * The same goes for process_vm_writev().
+ */
+static ssize_t strace_process_vm_writev(pid_t pid,
+		 const struct iovec *lvec,
+		 unsigned long liovcnt,
+		 const struct iovec *rvec,
+		 unsigned long riovcnt,
+		 unsigned long flags)
+{
+	return syscall(__NR_process_vm_writev, (long)pid, lvec, liovcnt, rvec, riovcnt, flags);
+}
+# define process_vm_writev strace_process_vm_writev
 #endif /* !HAVE_PROCESS_VM_READV */
 
 static ssize_t
@@ -987,6 +1001,29 @@ vm_read_mem(const pid_t pid, void *const laddr,
 	return process_vm_readv(pid, &local, 1, &remote, 1, 0);
 }
 
+static ssize_t
+vm_write_mem(const pid_t pid, const void *const laddr,
+	    const kernel_ulong_t raddr, const size_t len)
+{
+	const unsigned long truncated_raddr = raddr;
+
+	if (raddr != (kernel_ulong_t) truncated_raddr) {
+		errno = EIO;
+		return -1;
+	}
+
+	const struct iovec local = {
+		.iov_base = (void *) laddr,
+		.iov_len = len
+	};
+	const struct iovec remote = {
+		.iov_base = (void *) truncated_raddr,
+		.iov_len = len
+	};
+
+	return process_vm_writev(pid, &local, 1, &remote, 1, 0);
+}
+
 /*
  * move `len' bytes of data from process `pid'
  * at address `addr' to our space at `our_addr'
@@ -1283,6 +1320,141 @@ umovestr(struct tcb *const tcp, kernel_ulong_t addr, unsigned int len, char *lad
 	return 0;
 }
 
+static bool
+partial_poke(int pid, kernel_ulong_t addr, unsigned int len, const void *laddr,
+	     unsigned int off)
+{
+	union {
+		long val;
+		char x[sizeof(long)];
+	} u;
+	errno = 0;
+	u.val = ptrace(PTRACE_PEEKDATA, pid, addr, 0);
+	switch (errno) {
+		case 0:
+			break;
+		case ESRCH: case EINVAL:
+			/* these could be seen if the process is gone */
+			return false;
+		case EFAULT: case EIO: case EPERM:
+			/* address space is inaccessible */
+			return false;
+		default:
+			/* all the rest is strange and should be reported */
+			perror_msg("partial_poke: PTRACE_PEEKDATA pid:%d @0x%" PRI_klx,
+				    pid, addr);
+			return false;
+	}
+
+	memcpy(u.x + off, laddr, len);
+
+	/* now write it back */
+	if (ptrace(PTRACE_POKEDATA, pid, addr, u.val) < 0) {
+		switch (errno) {
+			case ESRCH: case EINVAL:
+				/* these could be seen if the process is gone */
+				return -1;
+			case EFAULT: case EIO: case EPERM:
+				/* address space is inaccessible, or write is prohibited */
+				return -1;
+			default:
+				/* all the rest is strange and should be reported */
+				perror_msg("partial_poke: PTRACE_POKEDATA pid:%d @0x%" PRI_klx,
+					    pid, addr);
+				return -1;
+		}
+	}
+
+	return true;
+}
+
+int
+upoken(struct tcb *tcp, kernel_ulong_t addr, unsigned int len,
+       const void *const our_addr)
+{
+	if (!len)
+		return 0;
+
+	const char *laddr = our_addr;
+	int pid = tcp->pid;
+
+#if ANY_WORDSIZE_LESS_THAN_KERNEL_LONG
+	if (current_wordsize < sizeof(addr)
+	    && (addr & (~(kernel_ulong_t) -1U))) {
+		return -1;
+	}
+#endif
+
+	if (!process_vm_readv_not_supported) {
+		int r = vm_write_mem(pid, laddr, addr, len);
+		if ((unsigned int) r == len)
+			return 0;
+		if (r >= 0) {
+			error_msg("upoken: short write (%u < %u) @0x%" PRI_klx,
+				  (unsigned int) r, len, addr);
+			return -1;
+		}
+		switch (errno) {
+			case ENOSYS:
+				process_vm_readv_not_supported = 1;
+				break;
+			case EPERM:
+				/* operation not permitted, try PTRACE_POKEDATA */
+				break;
+			case ESRCH:
+				/* the process is gone */
+				return -1;
+			case EFAULT: case EIO:
+				/* address space is inaccessible */
+				return -1;
+			default:
+				/* all the rest is strange and should be reported */
+				perror_msg("process_vm_writev");
+				return -1;
+		}
+	}
+
+	if (addr & (sizeof(long) - 1)) {
+		/* addr not a multiple of sizeof(long) */
+		unsigned n = addr & (sizeof(long) - 1);	/* residue */
+		addr &= -sizeof(long);			/* aligned address */
+		unsigned m = MIN(sizeof(long) - n, len);
+		if (!partial_poke(pid, addr, m, laddr, n))
+			return -1;
+		addr += sizeof(long);
+		laddr += m;
+		len -= m;
+	}
+
+	while (len >= sizeof(long)) {
+		if (ptrace(PTRACE_POKEDATA, pid, addr, * (const long *) laddr) < 0) {
+			switch (errno) {
+			case ESRCH: case EINVAL:
+				/* these could be seen if the process is gone */
+				return -1;
+			case EFAULT: case EIO: case EPERM:
+				/* address space is inaccessible, or write is prohibited */
+				return -1;
+			default:
+				/* all the rest is strange and should be reported */
+				perror_msg("upoken: PTRACE_POKEDATA pid:%d @0x%" PRI_klx,
+					    pid, addr);
+				return -1;
+			}
+		}
+		addr += sizeof(long);
+		laddr += sizeof(long);
+		len -= sizeof(long);
+	}
+
+	if (len) {
+		if (!partial_poke(pid, addr, len, laddr, 0))
+			return -1;
+	}
+
+	return 0;
+}
+
 /*
  * Iteratively fetch and print up to nmemb elements of elem_size size
  * from the array that starts at tracee's address start_addr.
-- 
2.11.0





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