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authorEric W. Biederman <ebiederm@xmission.com>2006-09-26 10:52:38 +0200
committerAndi Kleen <andi@basil.nowhere.org>2006-09-26 10:52:38 +0200
commit26374c7b7dca1ff90607c83d9b82e917119f0456 (patch)
treee2557e7b679eeee6d361b08812f9b10b96a301ec /arch/x86_64
parent0136611c62e8650e354b95c76dff6d2ce6030eff (diff)
[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')
-rw-r--r--arch/x86_64/kernel/head.S11
1 files changed, 7 insertions, 4 deletions
diff --git a/arch/x86_64/kernel/head.S b/arch/x86_64/kernel/head.S
index 4a3326ce709..1e6f8087067 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