linux-kernel - Re: [PATCH] x86/boot: Fix kexec booting failure after SEV early boot support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1a9e75fa-5105-f17d-e8f8-a3d2314c9680@amd.com>
Date:   Thu, 27 Sep 2018 13:16:57 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     Kairui Song <kasong@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "Singh, Brijesh" <brijesh.singh@....com>,
        "bp@...e.de" <bp@...e.de>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "dyoung@...hat.com" <dyoung@...hat.com>,
        "bhe@...hat.com" <bhe@...hat.com>,
        "ghook@...hat.com" <ghook@...hat.com>
Subject: Re: [PATCH] x86/boot: Fix kexec booting failure after SEV early boot
 support

On 09/27/2018 07:38 AM, Kairui Song wrote:
> Commit 1958b5fc4010 ("x86/boot: Add early boot support when running
> with SEV active") is causing kexec becomes sometimes unstable even if
> SEV is not active. kexec reboot won't start a second kernel bypassing
> BIOS boot process, instead, the system got reset.
> 
> That's because, in get_sev_encryption_bit function, we are using
> 32-bit RIP-relative addressing to read the value of enc_bit, but
> kexec may alloc the early boot up code to a higher location, which
> is beyond 32-bit addressing limit. Some garbage will be read and
> get_sev_encryption_bit will return the wrong value, which leads to
> wrong memory page flag.
> 
> This patch removes the use of enc_bit, as currently, enc_bit's only
> purpose is to avoid duplicated encryption bit reading, but the overhead
> of reading encryption bit is so tiny, so no need to cache that.
> 
> Fixes: 1958b5fc4010 ("x86/boot: Add early boot support when running with SEV active")
> Suggested-by: Borislav Petkov <bp@...e.de>
> Signed-off-by: Kairui Song <kasong@...hat.com>

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

> ---
>  arch/x86/boot/compressed/mem_encrypt.S | 19 -------------------
>  1 file changed, 19 deletions(-)
> 
> diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
> index eaa843a52907..a480356e0ed8 100644
> --- a/arch/x86/boot/compressed/mem_encrypt.S
> +++ b/arch/x86/boot/compressed/mem_encrypt.S
> @@ -25,20 +25,6 @@ ENTRY(get_sev_encryption_bit)
>  	push	%ebx
>  	push	%ecx
>  	push	%edx
> -	push	%edi
> -
> -	/*
> -	 * RIP-relative addressing is needed to access the encryption bit
> -	 * variable. Since we are running in 32-bit mode we need this call/pop
> -	 * sequence to get the proper relative addressing.
> -	 */
> -	call	1f
> -1:	popl	%edi
> -	subl	$1b, %edi
> -
> -	movl	enc_bit(%edi), %eax
> -	cmpl	$0, %eax
> -	jge	.Lsev_exit
>  
>  	/* Check if running under a hypervisor */
>  	movl	$1, %eax
> @@ -69,15 +55,12 @@ ENTRY(get_sev_encryption_bit)
>  
>  	movl	%ebx, %eax
>  	andl	$0x3f, %eax		/* Return the encryption bit location */
> -	movl	%eax, enc_bit(%edi)
>  	jmp	.Lsev_exit
>  
>  .Lno_sev:
>  	xor	%eax, %eax
> -	movl	%eax, enc_bit(%edi)
>  
>  .Lsev_exit:
> -	pop	%edi
>  	pop	%edx
>  	pop	%ecx
>  	pop	%ebx
> @@ -113,8 +96,6 @@ ENTRY(set_sev_encryption_mask)
>  ENDPROC(set_sev_encryption_mask)
>  
>  	.data
> -enc_bit:
> -	.int	0xffffffff
>  
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  	.balign	8
>