Re: [PATCH v2] x86/mm: Fix use of uninitialized buffer in sme_enable()

[Tom Lendacky]

On 3/6/23 10:06, Nikita Zhandarovich wrote:
> cmdline_find_option() may fail before doing any initialization of
> 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 -1.
>
> Found by Linux Verification Center (linuxtesting.org) with static analysis
> tool SVACE.
>
> Fixes: aca20d546214 ("x86/mm: Add support to make use of Secure Memory Encryption")
> Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>

Acked-by: Tom Lendacky <thomas.lendacky@xxxxxxx>

> ---
> v2: per Borislav Petkov's <bp@xxxxxxxxx> remarks:
> - return early if cmdline_find_options() fails with -1 instead of zeroing out
> buffer;
> - use correct Fixes: commit hash
>
>   arch/x86/mm/mem_encrypt_identity.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index 88cccd65029d..c6efcf559d88 100644
> --- 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;