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Re: [PATCH V3 04/49] x86/xen: Add xenpv_restore_regs_and_return_to_usermode()
- To: Lai Jiangshan <jiangshanlai@xxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Sat, 16 Oct 2021 14:08:55 -0400
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- Cc: x86@xxxxxxxxxx, Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Peter Anvin <hpa@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Andy Lutomirski <luto@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- Delivery-date: Sat, 16 Oct 2021 18:09:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10/13/21 11:13 PM, Lai Jiangshan wrote:
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
While in the native case, PER_CPU_VAR(cpu_tss_rw + TSS_sp0) is the
trampoline stack. But XEN pv doesn't use trampoline stack, so
PER_CPU_VAR(cpu_tss_rw + TSS_sp0) is also the kernel stack. Hence source
and destination stacks are identical in that case, which means reusing
swapgs_restore_regs_and_return_to_usermode() in XEN pv would cause %rsp
to move up to the top of the kernel stack and leave the IRET frame below
%rsp, which is dangerous to be corrupted if #NMI / #MC hit as either of
these events occurring in the middle of the stack pushing would clobber
data on the (original) stack.
And swapgs_restore_regs_and_return_to_usermode() pushing the IRET frame
on to the original address is useless and error-prone when there is any
future attempt to modify the code.
Fixes: 7f2590a110b8 ("x86/entry/64: Use a per-CPU trampoline stack for IDT
entries")
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Peter Anvin <hpa@xxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
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