xen/console: Don't treat NUL character as the end of the buffer

After upgrading Debian to Buster, I have began to notice console
mangling when using zsh in Dom0. This is happenning because output sent by
zsh to the console may contain NULs in the middle of the buffer.

The actual implementation of CONSOLEIO_write considers that a buffer
always terminate with a NUL and therefore will ignore anything after it.

In general, NULs are perfectly legitimate in terminal streams. For
instance, this could be used for padding slow terminals. See terminfo(5)
section `Delays and Padding`, or search for the pcre '\bpad'.

Other use cases includes using the console for dumping non-human
readable information (e.g debugger, file if no network...). With the
current behavior, the resulting stream will end up to be corrupted.

The documentation for CONSOLEIO_write is pretty limited (to not say
inexistent). From the declaration, the hypercall takes a buffer and size.
So this could lead to think the NUL character is allowed in the middle of
the buffer.

This patch updates the console API to pass the size along the buffer
down so we can remove the reliance on buffer terminating by a NUL
character.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/arm/early_printk.c

@@ -17,9 +17,10 @@
 void early_putch(char c);
 void early_flush(void);
 
-void early_puts(const char *s)
+void early_puts(const char *s, size_t nr)
 {
-    while (*s != '\0') {
+    while ( nr-- > 0 )
+    {
         if (*s == '\n')
             early_putch('\r');
         early_putch(*s);

xen/common/gdbstub.c

@@ -68,7 +68,7 @@ static void gdb_smp_resume(void);
 static char __initdata opt_gdb[30];
 string_param("gdb", opt_gdb);
 
-static void gdbstub_console_puts(const char *str);
+static void gdbstub_console_puts(const char *str, size_t nr);
 
 /* value <-> char (de)serialzers */
 static char
@@ -546,14 +546,14 @@ __gdb_ctx = {
 static struct gdb_context *gdb_ctx = &__gdb_ctx;
 
 static void
-gdbstub_console_puts(const char *str)
+gdbstub_console_puts(const char *str, size_t nr)
 {
     const char *p;
 
     gdb_start_packet(gdb_ctx);
     gdb_write_to_packet_char('O', gdb_ctx);
 
-    for ( p = str; *p != '\0'; p++ )
+    for ( p = str; nr > 0; p++, nr-- )
     {
         gdb_write_to_packet_char(hex2char((*p>>4) & 0x0f), gdb_ctx );
         gdb_write_to_packet_char(hex2char((*p) & 0x0f), gdb_ctx );

xen/drivers/char/console.c

@@ -326,9 +326,9 @@ long read_console_ring(struct xen_sysctl_readconsole *op)
 static char serial_rx_ring[SERIAL_RX_SIZE];
 static unsigned int serial_rx_cons, serial_rx_prod;
 
-static void (*serial_steal_fn)(const char *) = early_puts;
+static void (*serial_steal_fn)(const char *, size_t nr) = early_puts;
 
-int console_steal(int handle, void (*fn)(const char *))
+int console_steal(int handle, void (*fn)(const char *, size_t nr))
 {
     if ( (handle == -1) || (handle != sercon_handle) )
         return 0;
@@ -346,15 +346,15 @@ void console_giveback(int id)
         serial_steal_fn = NULL;
 }
 
-static void sercon_puts(const char *s)
+static void sercon_puts(const char *s, size_t nr)
 {
     if ( serial_steal_fn != NULL )
-        (*serial_steal_fn)(s);
+        serial_steal_fn(s, nr);
     else
-        serial_puts(sercon_handle, s);
+        serial_puts(sercon_handle, s, nr);
 
     /* Copy all serial output into PV console */
-    pv_console_puts(s);
+    pv_console_puts(s, nr);
 }
 
 static void dump_console_ring_key(unsigned char key)
@@ -387,10 +387,9 @@ static void dump_console_ring_key(unsigned char key)
         sofar += len;
         c += len;
     }
-    buf[sofar] = '\0';
 
-    sercon_puts(buf);
-    video_puts(buf);
+    sercon_puts(buf, sofar);
+    video_puts(buf, sofar);
 
     free_xenheap_pages(buf, order);
 }
@@ -528,7 +527,7 @@ static inline void xen_console_write_debug_port(const char *buf, size_t len)
 static long guest_console_write(XEN_GUEST_HANDLE_PARAM(char) buffer, int count)
 {
     char kbuf[128];
-    int kcount = 0;
+    unsigned int kcount = 0;
     struct domain *cd = current->domain;
 
     while ( count > 0 )
@@ -541,25 +540,22 @@ static long guest_console_write(XEN_GUEST_HANDLE_PARAM(char) buffer, int count)
         kcount = min_t(int, count, sizeof(kbuf)-1);
         if ( copy_from_guest(kbuf, buffer, kcount) )
             return -EFAULT;
-        kbuf[kcount] = '\0';
 
         if ( is_hardware_domain(cd) )
         {
             /* Use direct console output as it could be interactive */
             spin_lock_irq(&console_lock);
 
-            sercon_puts(kbuf);
-            video_puts(kbuf);
+            sercon_puts(kbuf, kcount);
+            video_puts(kbuf, kcount);
 
 #ifdef CONFIG_X86
             if ( opt_console_xen )
             {
-                size_t len = strlen(kbuf);
-
                 if ( xen_guest )
-                    xen_hypercall_console_write(kbuf, len);
+                    xen_hypercall_console_write(kbuf, kcount);
                 else
-                    xen_console_write_debug_port(kbuf, len);
+                    xen_console_write_debug_port(kbuf, kcount);
             }
 #endif
 
@@ -576,19 +572,20 @@ static long guest_console_write(XEN_GUEST_HANDLE_PARAM(char) buffer, int count)
             char *kin = kbuf, *kout = kbuf, c;
 
             /* Strip non-printable characters */
-            for ( ; ; )
+            do
             {
                 c = *kin++;
-                if ( c == '\0' || c == '\n' )
+                if ( c == '\n' )
                     break;
                 if ( isprint(c) || c == '\t' )
                     *kout++ = c;
-            }
+            } while ( --kcount > 0 );
+
             *kout = '\0';
             spin_lock(&cd->pbuf_lock);
+            kcount = kin - kbuf;
             if ( c == '\n' )
             {
-                kcount = kin - kbuf;
                 cd->pbuf[cd->pbuf_idx] = '\0';
                 guest_printk(cd, XENLOG_G_DEBUG "%s%s\n", cd->pbuf, kbuf);
                 cd->pbuf_idx = 0;
@@ -667,16 +664,16 @@ static bool_t console_locks_busted;
 
 static void __putstr(const char *str)
 {
+    size_t len = strlen(str);
+
     ASSERT(spin_is_locked(&console_lock));
 
-    sercon_puts(str);
-    video_puts(str);
+    sercon_puts(str, len);
+    video_puts(str, len);
 
 #ifdef CONFIG_X86
     if ( opt_console_xen )
     {
-        size_t len = strlen(str);
-
         if ( xen_guest )
             xen_hypercall_console_write(str, len);
         else
@@ -1250,6 +1247,7 @@ void debugtrace_printk(const char *fmt, ...)
     char          cntbuf[24];
     va_list       args;
     unsigned long flags;
+    unsigned int nr;
 
     if ( debugtrace_bytes == 0 )
         return;
@@ -1261,14 +1259,15 @@ void debugtrace_printk(const char *fmt, ...)
     ASSERT(debugtrace_buf[debugtrace_bytes - 1] == 0);
 
     va_start(args, fmt);
-    vsnprintf(buf, sizeof(buf), fmt, args);
+    nr = vscnprintf(buf, sizeof(buf), fmt, args);
     va_end(args);
 
     if ( debugtrace_send_to_console )
     {
-        snprintf(cntbuf, sizeof(cntbuf), "%u ", ++count);
-        serial_puts(sercon_handle, cntbuf);
-        serial_puts(sercon_handle, buf);
+        unsigned int n = scnprintf(cntbuf, sizeof(cntbuf), "%u ", ++count);
+
+        serial_puts(sercon_handle, cntbuf, n);
+        serial_puts(sercon_handle, buf, nr);
     }
     else
     {
@@ -1381,7 +1380,7 @@ void panic(const char *fmt, ...)
  * **************************************************************
  */
 
-static void suspend_steal_fn(const char *str) { }
+static void suspend_steal_fn(const char *str, size_t nr) { }
 static int suspend_steal_id;
 
 int console_suspend(void)

xen/drivers/char/consoled.c

@@ -77,16 +77,13 @@ size_t consoled_guest_rx(void)
 
         if ( idx >= BUF_SZ )
         {
-            pv_console_puts(buf);
+            pv_console_puts(buf, BUF_SZ);
             idx = 0;
         }
     }
 
     if ( idx )
-    {
-        buf[idx] = '\0';
-        pv_console_puts(buf);
-    }
+        pv_console_puts(buf, idx);
 
     /* No need for a mem barrier because every character was already consumed */
     barrier();

xen/drivers/char/serial.c

@@ -223,11 +223,10 @@ void serial_putc(int handle, char c)
     spin_unlock_irqrestore(&port->tx_lock, flags);
 }
 
-void serial_puts(int handle, const char *s)
+void serial_puts(int handle, const char *s, size_t nr)
 {
     struct serial_port *port;
     unsigned long flags;
-    char c;
 
     if ( handle == -1 )
         return;
@@ -238,8 +237,10 @@ void serial_puts(int handle, const char *s)
 
     spin_lock_irqsave(&port->tx_lock, flags);
 
-    while ( (c = *s++) != '\0' )
+    for ( ; nr > 0; nr--, s++ )
     {
+        char c = *s;
+
         if ( (c == '\n') && (handle & SERHND_COOKED) )
             __serial_putc(port, '\r' | ((handle & SERHND_HI) ? 0x80 : 0x00));
 

xen/drivers/char/xen_pv_console.c

@@ -129,13 +129,13 @@ size_t pv_console_rx(struct cpu_user_regs *regs)
     return recv;
 }
 
-static size_t pv_ring_puts(const char *buf)
+static size_t pv_ring_puts(const char *buf, size_t nr)
 {
     XENCONS_RING_IDX cons, prod;
     size_t sent = 0, avail;
     bool put_r = false;
 
-    while ( buf[sent] != '\0' || put_r )
+    while ( sent < nr || put_r )
     {
         cons = ACCESS_ONCE(cons_ring->out_cons);
         prod = cons_ring->out_prod;
@@ -156,7 +156,7 @@ static size_t pv_ring_puts(const char *buf)
             continue;
         }
 
-        while ( avail && (buf[sent] != '\0' || put_r) )
+        while ( avail && (sent < nr || put_r) )
         {
             if ( put_r )
             {
@@ -185,7 +185,7 @@ static size_t pv_ring_puts(const char *buf)
     return sent;
 }
 
-void pv_console_puts(const char *buf)
+void pv_console_puts(const char *buf, size_t nr)
 {
     unsigned long flags;
 
@@ -193,7 +193,7 @@ void pv_console_puts(const char *buf)
         return;
 
     spin_lock_irqsave(&tx_lock, flags);
-    pv_ring_puts(buf);
+    pv_ring_puts(buf, nr);
     spin_unlock_irqrestore(&tx_lock, flags);
 }
 

xen/drivers/video/lfb.c

@@ -53,14 +53,15 @@ static void lfb_show_line(
 }
 
 /* Fast mode which redraws all modified parts of a 2D text buffer. */
-void lfb_redraw_puts(const char *s)
+void lfb_redraw_puts(const char *s, size_t nr)
 {
     unsigned int i, min_redraw_y = lfb.ypos;
-    char c;
 
     /* Paste characters into text buffer. */
-    while ( (c = *s++) != '\0' )
+    for ( ; nr > 0; nr--, s++ )
     {
+        char c = *s;
+
         if ( (c == '\n') || (lfb.xpos >= lfb.lfbp.text_columns) )
         {
             if ( ++lfb.ypos >= lfb.lfbp.text_rows )
@@ -97,13 +98,14 @@ void lfb_redraw_puts(const char *s)
 }
 
 /* Slower line-based scroll mode which interacts better with dom0. */
-void lfb_scroll_puts(const char *s)
+void lfb_scroll_puts(const char *s, size_t nr)
 {
     unsigned int i;
-    char c;
 
-    while ( (c = *s++) != '\0' )
+    for ( ; nr > 0; nr--, s++ )
     {
+        char c = *s;
+
         if ( (c == '\n') || (lfb.xpos >= lfb.lfbp.text_columns) )
         {
             unsigned int bytes = (lfb.lfbp.width *

xen/drivers/video/lfb.h

@@ -35,8 +35,8 @@ struct lfb_prop {
     unsigned int text_rows;
 };
 
-void lfb_redraw_puts(const char *s);
-void lfb_scroll_puts(const char *s);
+void lfb_redraw_puts(const char *s, size_t nr);
+void lfb_scroll_puts(const char *s, size_t nr);
 void lfb_carriage_return(void);
 void lfb_free(void);
 

xen/drivers/video/vga.c

@@ -18,9 +18,9 @@ static int vgacon_keep;
 static unsigned int xpos, ypos;
 static unsigned char *video;
 
-static void vga_text_puts(const char *s);
-static void vga_noop_puts(const char *s) {}
-void (*video_puts)(const char *) = vga_noop_puts;
+static void vga_text_puts(const char *s, size_t nr);
+static void vga_noop_puts(const char *s, size_t nr) {}
+void (*video_puts)(const char *, size_t nr) = vga_noop_puts;
 
 /*
  * 'vga=<mode-specifier>[,keep]' where <mode-specifier> is one of:
@@ -174,12 +174,12 @@ void __init video_endboot(void)
     }
 }
 
-static void vga_text_puts(const char *s)
+static void vga_text_puts(const char *s, size_t nr)
 {
-    char c;
-
-    while ( (c = *s++) != '\0' )
+    for ( ; nr > 0; nr--, s++ )
     {
+        char c = *s;
+
         if ( (c == '\n') || (xpos >= columns) )
         {
             if ( ++ypos >= lines )

xen/include/xen/console.h

@@ -38,7 +38,7 @@ struct domain *console_input_domain(void);
  * Steal output from the console. Returns +ve identifier, else -ve error.
  * Takes the handle of the serial line to steal, and steal callback function.
  */
-int console_steal(int handle, void (*fn)(const char *));
+int console_steal(int handle, void (*fn)(const char *, size_t nr));
 
 /* Give back stolen console. Takes the identifier returned by console_steal. */
 void console_giveback(int id);

xen/include/xen/early_printk.h

@@ -5,7 +5,7 @@
 #define __XEN_EARLY_PRINTK_H__
 
 #ifdef CONFIG_EARLY_PRINTK
-void early_puts(const char *s);
+void early_puts(const char *s, size_t nr);
 #else
 #define early_puts NULL
 #endif

xen/include/xen/pv_console.h

@@ -8,7 +8,7 @@
 void pv_console_init(void);
 void pv_console_set_rx_handler(serial_rx_fn fn);
 void pv_console_init_postirq(void);
-void pv_console_puts(const char *buf);
+void pv_console_puts(const char *buf, size_t nr);
 size_t pv_console_rx(struct cpu_user_regs *regs);
 evtchn_port_t pv_console_evtchn(void);
 
@@ -17,7 +17,7 @@ evtchn_port_t pv_console_evtchn(void);
 static inline void pv_console_init(void) {}
 static inline void pv_console_set_rx_handler(serial_rx_fn fn) { }
 static inline void pv_console_init_postirq(void) { }
-static inline void pv_console_puts(const char *buf) { }
+static inline void pv_console_puts(const char *buf, size_t nr) { }
 static inline size_t pv_console_rx(struct cpu_user_regs *regs) { return 0; }
 evtchn_port_t pv_console_evtchn(void)
 {

xen/include/xen/serial.h

@@ -114,8 +114,8 @@ int serial_parse_handle(char *conf);
 /* Transmit a single character via the specified COM port. */
 void serial_putc(int handle, char c);
 
-/* Transmit a NULL-terminated string via the specified COM port. */
-void serial_puts(int handle, const char *s);
+/* Transmit a string via the specified COM port. */
+void serial_puts(int handle, const char *s, size_t nr);
 
 /*
  * An alternative to registering a character-receive hook. This function

xen/include/xen/video.h

@@ -13,11 +13,11 @@
 
 #ifdef CONFIG_VIDEO
 void video_init(void);
-extern void (*video_puts)(const char *);
+extern void (*video_puts)(const char *, size_t nr);
 void video_endboot(void);
 #else
 #define video_init()    ((void)0)
-#define video_puts(s)   ((void)0)
+static inline void video_puts(const char *str, size_t nr) {}
 #define video_endboot() ((void)0)
 #endif