x86/mm: Fix use of uninitialized buffer in sme_enable()

stable inclusion
from stable-v4.19.279
commit ffdf8d81c48822a329af9f31dc239090f4a60761
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6TIG1
CVE: NA

--------------------------------

commit cbebd68f upstream.

cmdline_find_option() may fail before doing any initialization of
the buffer array. This may lead to unpredictable results when the same
buffer is used later in calls to strncmp() function.  Fix the issue by
returning early if cmdline_find_option() returns an error.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: aca20d54 ("x86/mm: Add support to make use of Secure Memory Encryption")
Signed-off-by: NNikita Zhandarovich <n.zhandarovich@fintech.ru>
Signed-off-by: NBorislav Petkov (AMD) <bp@alien8.de>
Acked-by: NTom Lendacky <thomas.lendacky@amd.com>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/20230306160656.14844-1-n.zhandarovich@fintech.ruSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

arch/x86/mm/mem_encrypt_identity.c

@@ -563,7 +563,8 @@ void __init sme_enable(struct boot_params *bp)
 	cmdline_ptr = (const char *)((u64)bp->hdr.cmd_line_ptr |
 				     ((u64)bp->ext_cmd_line_ptr << 32));
 
-	cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer));
+	if (cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer)) < 0)
+		return;
 
 	if (!strncmp(buffer, cmdline_on, sizeof(buffer)))
 		sme_me_mask = me_mask;