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| author | Eric W. Biederman <ebiederm@xmission.com> | 2006-09-26 10:52:38 +0200 |
|---|---|---|
| committer | Andi Kleen <andi@basil.nowhere.org> | 2006-09-26 10:52:38 +0200 |
| commit | 26374c7b7dca1ff90607c83d9b82e917119f0456 (patch) | |
| tree | e2557e7b679eeee6d361b08812f9b10b96a301ec /arch/x86_64/kernel/head.S | |
| parent | [PATCH] optimize hweight64 for x86_64 (diff) | |
| download | linux-26374c7b7dca1ff90607c83d9b82e917119f0456.tar.xz linux-26374c7b7dca1ff90607c83d9b82e917119f0456.zip | |
[PATCH] Reload CS when startup_64 is used.
In long mode the %cs is largely a relic. However there are a few cases
like iret 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>
Signed-off-by: Andi Kleen <ak@suse.de>
Diffstat (limited to 'arch/x86_64/kernel/head.S')
| -rw-r--r-- | arch/x86_64/kernel/head.S | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/arch/x86_64/kernel/head.S b/arch/x86_64/kernel/head.S index 4a3326ce709c..1e6f80870679 100644 --- a/arch/x86_64/kernel/head.S +++ b/arch/x86_64/kernel/head.S @@ -185,12 +185,15 @@ startup_64: /* 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 + * to the full 64bit address, this is only possible as indirect + * jump. In addition we need to ensure %cs is set so we make this + * a far return. */ movq initial_code(%rip),%rax - pushq $0 # fake return address - jmp *%rax + pushq $0 # fake return address to stop unwinder + pushq $__KERNEL_CS # set correct cs + pushq %rax # target address in negative space + lretq /* SMP bootup changes these two */ .align 8 |