Messages in this thread Patch in this message |  | | | From | (Eric W. Biederman) | | Subject | [PATCH] x86_64: Reload CS when startup_64 is used. | | Date | Tue, 22 Aug 2006 02:37:44 -0600 |
| |
In long mode the %cs is largely a relic. However there are a few cases like lret where it matters that we have a valid value. Without this patch it is possible to enter the kernel in startup_64 without setting %cs to a valid value. With this patch we don't care what %cs value we enter the kernel with, so long as the cs shadow register indicates it is a privileged code segment.
Thanks to Magnus Damm for finding this problem and posting the first workable patch. I have moved the jump to set %cs down a few instructions so we don't need to take an extra jump. Which keeps the code simpler.
Signed-of-by: Eric W. Biederman <ebiederm@xmission.com> --- arch/x86_64/kernel/head.S | 7 +++++-- 1 files changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86_64/kernel/head.S b/arch/x86_64/kernel/head.S index 923f080..6c89f6a 100644 --- a/arch/x86_64/kernel/head.S +++ b/arch/x86_64/kernel/head.S @@ -186,10 +186,13 @@ #define CR0_PAGING (1<<31) /* Finally jump to run C code and to be on real kernel address * Since we are running on identity-mapped space we have to jump * to the full 64bit address , this is only possible as indirect - * jump + * jump. In addition we need to ensure %cs is set so we make this + * a far return. */ movq initial_code(%rip),%rax - jmp *%rax + pushq $__KERNEL_CS + pushq %rax + lretq /* SMP bootup changes these two */ .align 8 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |