x86/microcode/amd: Fix snprintf() format string warning in W=1 build

Building with GCC 11.x results in the following warning:

  arch/x86/kernel/cpu/microcode/amd.c: In function ‘find_blobs_in_containers’:
  arch/x86/kernel/cpu/microcode/amd.c:504:58: error: ‘h.bin’ directive output may be truncated writing 5 bytes into a region of size between 1 and 7 [-Werror=format-truncation=]
  arch/x86/kernel/cpu/microcode/amd.c:503:17: note: ‘snprintf’ output between 35 and 41 bytes into a destination of size 36

The issue is that GCC does not know that the family can only be a byte
(it ultimately comes from CPUID).  Suggest the right size to the compiler
by marking the argument as char-size ("hh").  While at it, instead of
using the slightly more obscure precision specifier use the width with
zero padding (over 23000 occurrences in kernel sources, vs 500 for
the idiom using the precision).

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Closes: https://lore.kernel.org/oe-kbuild-all/202308252255.2HPJ6x5Q-lkp@intel.com/
Link: https://lore.kernel.org/r/20231016224858.2829248-1-pbonzini@redhat.com

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index bbd1dc3..b4eea8a 100644 (file)
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -501,7 +501,7 @@ static bool get_builtin_microcode(struct cpio_data *cp, unsigned int family)
 
        if (family >= 0x15)
                snprintf(fw_name, sizeof(fw_name),
-                        "amd-ucode/microcode_amd_fam%.2xh.bin", family);
+                        "amd-ucode/microcode_amd_fam%02hhxh.bin", family);
 
        if (firmware_request_builtin(&fw, fw_name)) {
                cp->size = fw.size;