linux-kernel - Re: [PATCH v2] x86/mm: Fix use of uninitialized buffer in sme

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Date:   Mon, 13 Mar 2023 07:49:36 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Nikita Zhandarovich <n.zhandarovich@...tech.ru>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH v2] x86/mm: Fix use of uninitialized buffer in
 sme_enable()

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@...tech.ru>

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

> ---
> v2: per Borislav Petkov's <bp@...en8.de> 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;