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x86/bugs, KVM: Support the combination of guest and host IBRS

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A guest may modify the SPEC_CTRL MSR from the value used by the
kernel. Since the kernel doesn't use IBRS, this means a value of zero is
what is needed in the host.

But the 336996-Speculative-Execution-Side-Channel-Mitigations.pdf refers to
the other bits as reserved so the kernel should respect the boot time
SPEC_CTRL value and use that.

This allows to deal with future extensions to the SPEC_CTRL interface if
any at all.

Note: This uses wrmsrl() instead of native_wrmsl(). I does not make any
difference as paravirt will over-write the callq *0xfff.. with the wrmsrl
assembler code.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Konrad Rzeszutek Wilk
2018-04-25 22:04:19 -04:00
committed by Thomas Gleixner
parent 1b86883ccb
commit 5cf6875487
4 changed files with 32 additions and 8 deletions
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10
arch/x86/include/asm/nospec-branch.h
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@@ -228,6 +228,16 @@ enum spectre_v2_mitigation {
extern void x86_spec_ctrl_set(u64);
extern u64 x86_spec_ctrl_get_default(void);
/*
* On VMENTER we must preserve whatever view of the SPEC_CTRL MSR
* the guest has, while on VMEXIT we restore the host view. This
* would be easier if SPEC_CTRL were architecturally maskable or
* shadowable for guests but this is not (currently) the case.
* Takes the guest view of SPEC_CTRL MSR as a parameter.
*/
extern void x86_spec_ctrl_set_guest(u64);
extern void x86_spec_ctrl_restore_host(u64);
extern char __indirect_thunk_start[];
extern char __indirect_thunk_end[];