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

commit ae54034f633c55dd9fe47d979ae6ebef7f18f192 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: a7568920e52f ("x86/mm: Add support to make use of Secure Memory Encryption")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@fintech.ru>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/20230306160656.14844-1-n.zhandarovich@fintech.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index f415498d3175cf7f67eef6f20c72a5f247a24a2f..d94ebd8acdfdecdcdff836ca0351dde63f11ecb7 100644 (file)
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -600,7 +600,8 @@ 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;