linux-kernel - Re: [PATCH v3 3/5] x86/boot/compressed/64: Check SEV encryption in 64-bit boot-path

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Message-ID: <20201027110945.GD15580@zn.tnic>
Date:   Tue, 27 Oct 2020 12:09:45 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, Joerg Roedel <jroedel@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Martin Radev <martin.b.radev@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/5] x86/boot/compressed/64: Check SEV encryption in
 64-bit boot-path

On Wed, Oct 21, 2020 at 02:39:36PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> Check whether the hypervisor reported the correct C-bit when running as
> an SEV guest. Using a wrong C-bit position could be used to leak
> sensitive data from the guest to the hypervisor.
> 
> The check function is in arch/x86/kernel/sev_verify_cbit.S so that it
> can be re-used in the running kernel image.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
>  arch/x86/boot/compressed/ident_map_64.c |  1 +
>  arch/x86/boot/compressed/mem_encrypt.S  |  4 ++
>  arch/x86/boot/compressed/misc.h         |  2 +
>  arch/x86/kernel/sev_verify_cbit.S       | 90 +++++++++++++++++++++++++
>  4 files changed, 97 insertions(+)
>  create mode 100644 arch/x86/kernel/sev_verify_cbit.S
> 
> diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
> index 063a60edcf99..73abba3312a7 100644
> --- a/arch/x86/boot/compressed/ident_map_64.c
> +++ b/arch/x86/boot/compressed/ident_map_64.c
> @@ -153,6 +153,7 @@ void initialize_identity_maps(void)
>  	 * into cr3.
>  	 */
>  	add_identity_map((unsigned long)_head, (unsigned long)_end);
> +	sev_verify_cbit(top_level_pgt);
>  	write_cr3(top_level_pgt);
>  }

Btw, might wanna redo them ontop of -rc1 because this looks like this after
Arvind's three fixes:

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index a5e5db6ada3c..81f6003553f8 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -162,6 +162,7 @@ void initialize_identity_maps(void *rmode)
        add_identity_map((unsigned long)boot_params, (unsigned long)(boot_params + 1));
        cmdline = get_cmd_line_ptr();
        add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE);
+       sev_verify_cbit(top_level_pgt);
 
        /* Load the new page-table. */
        write_cr3(top_level_pgt);


-- 
Regards/Gruss,
    Boris.

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