diff mbox series

[v8,24/33] x86/fred: disallow the swapgs instruction when FRED is enabled

Message ID 20230410081438.1750-25-xin3.li@intel.com
State New
Headers
Series x86: enable FRED for x86-64 |

Commit Message

Li, Xin3 April 10, 2023, 8:14 a.m. UTC 
  From: "H. Peter Anvin (Intel)" <hpa@zytor.com>

The FRED architecture establishes the full supervisor/user through:
1) FRED event delivery swaps the value of the GS base address and
   that of the IA32_KERNEL_GS_BASE MSR.
2) ERETU swaps the value of the GS base address and that of the
   IA32_KERNEL_GS_BASE MSR.
Thus, the swapgs instruction is disallowed when FRED is enabled,
otherwise it causes #UD.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Tested-by: Shan Kang <shan.kang@intel.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
 arch/x86/kernel/process_64.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Thomas Gleixner June 5, 2023, 1:47 p.m. UTC | #1 
On Mon, Apr 10 2023 at 01:14, Xin Li wrote:
> From: "H. Peter Anvin (Intel)" <hpa@zytor.com>
>
> The FRED architecture establishes the full supervisor/user through:
> 1) FRED event delivery swaps the value of the GS base address and
>    that of the IA32_KERNEL_GS_BASE MSR.
> 2) ERETU swaps the value of the GS base address and that of the
>    IA32_KERNEL_GS_BASE MSR.
> Thus, the swapgs instruction is disallowed when FRED is enabled,
> otherwise it causes #UD.

Which does not explain why writing directly to the IA32_KERNEL_GS_BASE
MSR is doing the right thing.

Thanks,

        tglx
diff mbox series

Patch

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index a1aa74864c8b..2bea86073646 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -165,7 +165,8 @@  static noinstr unsigned long __rdgsbase_inactive(void)
 
 	lockdep_assert_irqs_disabled();
 
-	if (!cpu_feature_enabled(X86_FEATURE_XENPV)) {
+	if (!cpu_feature_enabled(X86_FEATURE_FRED) &&
+	    !cpu_feature_enabled(X86_FEATURE_XENPV)) {
 		native_swapgs();
 		gsbase = rdgsbase();
 		native_swapgs();
@@ -190,7 +191,8 @@  static noinstr void __wrgsbase_inactive(unsigned long gsbase)
 {
 	lockdep_assert_irqs_disabled();
 
-	if (!cpu_feature_enabled(X86_FEATURE_XENPV)) {
+	if (!cpu_feature_enabled(X86_FEATURE_FRED) &&
+	    !cpu_feature_enabled(X86_FEATURE_XENPV)) {
 		native_swapgs();
 		wrgsbase(gsbase);
 		native_swapgs();