From: "Lendacky, Thomas" <Thomas.Lendacky@amd.com>
To: Kairui Song <kasong@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: "tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"x86@kernel.org" <x86@kernel.org>,
"Singh, Brijesh" <brijesh.singh@amd.com>,
"bp@suse.de" <bp@suse.de>,
"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
"dyoung@redhat.com" <dyoung@redhat.com>,
"bhe@redhat.com" <bhe@redhat.com>,
"ghook@redhat.com" <ghook@redhat.com>
Subject: Re: [PATCH] x86/boot: Fix kexec booting failure after SEV early boot support
Date: Thu, 27 Sep 2018 13:16:57 +0000 [thread overview]
Message-ID: <1a9e75fa-5105-f17d-e8f8-a3d2314c9680@amd.com> (raw)
In-Reply-To: <20180927123845.32052-1-kasong@redhat.com>
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@suse.de>
> Signed-off-by: Kairui Song <kasong@redhat.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.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
>
next prev parent reply other threads:[~2018-09-27 13:17 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-27 12:38 [PATCH] x86/boot: Fix kexec booting failure after SEV early boot support Kairui Song
2018-09-27 13:16 ` Lendacky, Thomas [this message]
2018-09-27 19:06 ` [tip:x86/urgent] x86/boot: Fix kexec booting failure in the SEV bit detection code tip-bot for Kairui Song
-- strict thread matches above, loose matches on Subject: below --
2018-09-25 11:10 [PATCH] x86/boot: Fix kexec booting failure after SEV early boot support Kairui Song
2018-09-25 14:33 ` Lendacky, Thomas
2018-09-25 17:26 ` Borislav Petkov
2018-09-26 7:32 ` Baoquan He
2018-09-26 10:52 ` Kairui Song
2018-09-26 11:22 ` Baoquan He
2018-09-26 13:01 ` Lendacky, Thomas
2018-09-26 13:18 ` Borislav Petkov
2018-09-26 13:21 ` Baoquan He
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