On Thu, Mar 3, 2016 at 4:28 AM, Borislav Petkov <b...@alien8.de> wrote:
> 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
> 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.
>
> 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
> --
> 2.3.5
I would suggest moving down verify_cpu calling after offset is
calcuated, like following instead of adding __end_init_task.
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 22fbf9d..e8c8085 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -64,9 +64,6 @@ startup_64:
* tables and then reload them.
*/
- /* Sanitize CPU configuration */
- call verify_cpu
-
/*
* Compute the delta between the address I am compiled to run at and the
* address I am actually running at.
@@ -74,6 +71,14 @@ startup_64:
leaq _text(%rip), %rbp
subq $_text - __START_KERNEL_map, %rbp
+ /* Setup stack for verify_cpu() */
+ movq stack_start(%rip), %rsp
+ subq $__START_KERNEL_map, %rsp
+ addq %rbp, %rsp
+
+ /* Sanitize CPU configuration */
+ call verify_cpu
+
/* Is the address not 2M aligned? */
testl $~PMD_PAGE_MASK, %ebp
jnz bad_address
