On March 3, 2016 4:28:36 AM PST, Borislav Petkov <b...@alien8.de> wrote:
>On Wed, Mar 02, 2016 at 02:32:54PM -0800, H. Peter Anvin wrote:
>> I'm trying to think of any reason why we couldn't simply have a
>symbol
>> at the top of the initial stack? Then a simple leaq would suffice;
>> this is for the BSP after all.
>
>How about something like this:
>
>---
>From: Borislav Petkov <b...@suse.de>
>Date: Sun, 28 Feb 2016 21:35:44 +0100
>Subject: [PATCH -v2] x86/asm: Make sure verify_cpu() has a good stack
>MIME-Version: 1.0
>Content-Type: text/plain; charset=UTF-8
>Content-Transfer-Encoding: 8bit
>
>04633df0c43d ("x86/cpu: Call verify_cpu() after having entered long
>mode too")
>added the call to verify_cpu() for sanitizing CPU configuration.
>
>The latter uses the stack minimally and it can happen that we land in
>startup_64() directly from a 64-bit bootloader. Then we want to use our
>own, known good stack.
>
>Do that.
>
>APs don't need this as the trampoline sets up a stack for them.
>
>Reported-by: Tom Lendacky <thomas.lenda...@amd.com>
>Signed-off-by: Borislav Petkov <b...@suse.de>
>Cc: Brian Gerst <brge...@gmail.com>
>Cc: "H. Peter Anvin" <h...@zytor.com>
>Cc: Mika Penttilä <mika.pentt...@nextfour.com>
>---
> arch/x86/kernel/head_64.S | 3 +++
> include/asm-generic/vmlinux.lds.h | 4 +++-
> 2 files changed, 6 insertions(+), 1 deletion(-)
>
>diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
>index 22fbf9df61bb..968d6408b887 100644
>--- a/arch/x86/kernel/head_64.S
>+++ b/arch/x86/kernel/head_64.S
>@@ -64,6 +64,9 @@ startup_64:
> * tables and then reload them.
> */
>
>+ /* Setup stack for verify_cpu(). */
>+ leaq (__end_init_task - 8)(%rip), %rsp
>+
> /* Sanitize CPU configuration */
> call verify_cpu
>
>diff --git a/include/asm-generic/vmlinux.lds.h
>b/include/asm-generic/vmlinux.lds.h
>index 772c784ba763..cba2a26628fc 100644
>--- a/include/asm-generic/vmlinux.lds.h
>+++ b/include/asm-generic/vmlinux.lds.h
>@@ -246,7 +246,9 @@
>
> #define INIT_TASK_DATA(align) \
> . = ALIGN(align); \
>- *(.data..init_task)
>+ VMLINUX_SYMBOL(__start_init_task) = .; \
>+ *(.data..init_task) \
>+ VMLINUX_SYMBOL(__end_init_task) = .;
>
> /*
> * Read only Data
Why -8?
--
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