[Minios-devel] [UNIKRAFT PATCH] plat/kvm: x86: Use `strncpy()` to retrieve cmdline

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Use `strncpy()` to retrieve the command line in KVM. This is to
simplify the routine. Additionally, this commit fixes an overflow bug
that happened when CONFIG_UK_NAME was bigger than the reserved memory
space for the command line.

Signed-off-by: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
---
 plat/kvm/x86/setup.c | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/plat/kvm/x86/setup.c b/plat/kvm/x86/setup.c
index 4ccd9470..df25592f 100644
--- a/plat/kvm/x86/setup.c
+++ b/plat/kvm/x86/setup.c
@@ -53,29 +53,25 @@ void *_libkvmplat_mem_end;
 extern void _libkvmplat_newstack(__u64 stack_start, void (*tramp)(void *),
                                void *arg);
 
-static inline void _mb_get_cmdline(struct multiboot_info *mi, char *cmdline,
-                                  size_t maxlen)
+static inline void _mb_get_cmdline(struct multiboot_info *mi)
 {
-       size_t cmdline_len;
        char *mi_cmdline;
 
        if (mi->flags & MULTIBOOT_INFO_CMDLINE) {
                mi_cmdline = (char *)(__u64)mi->cmdline;
-               cmdline_len = strlen(mi_cmdline);
 
-               if (cmdline_len >= maxlen) {
-                       cmdline_len = maxlen - 1;
-                       uk_pr_info("Command line too long, truncated\n");
-               }
-               memcpy(cmdline, mi_cmdline, cmdline_len);
-
-               /* ensure null termination */
-               cmdline[cmdline_len <= (maxlen - 1) ? cmdline_len
-                       : (maxlen - 1)] = '\0';
+               if (strlen(mi_cmdline) > sizeof(cmdline) - 1)
+                       uk_pr_err("Command line too long, truncated\n");
+               strncpy(cmdline, mi_cmdline,
+                       sizeof(cmdline));
        } else {
-               uk_pr_info("No command line found\n");
-               strcpy(cmdline, CONFIG_UK_NAME);
+               /* Use image name as cmdline to provide argv[0] */
+               uk_pr_debug("No command line present\n");
+               strncpy(cmdline, CONFIG_UK_NAME, sizeof(cmdline));
        }
+
+       /* ensure null termination */
+       cmdline[(sizeof(cmdline) - 1)] = '\0';
 }
 
 static inline void _mb_init_mem(struct multiboot_info *mi)
@@ -131,7 +127,7 @@ void _libkvmplat_entry(void *arg)
         * The multiboot structures may be anywhere in memory, so take a copy of
         * everything necessary before we initialise memory allocation.
         */
-       _mb_get_cmdline(mi, cmdline, sizeof(cmdline));
+       _mb_get_cmdline(mi);
        _mb_init_mem(mi);
 
        uk_pr_info("    heap start: %p\n", _libkvmplat_heap_start);
-- 
2.21.0


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