Re: Stable bugfix backport request of "KVM: x86: smm: preserve interrupt shadow in SMRAM"?

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On 1/26/24 16:20, Dongli Zhang wrote:
> Hi Maxim and Paolo, 
> 
> This is the linux-stable backport request regarding the below patch.
> 
> KVM: x86: smm: preserve interrupt shadow in SMRAM
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fb28875fd7da184079150295da7ee8d80a70917e
> 
> According to the below link, there may be a backport to stable kernels, while I
> do not see it in the stable kernels.
> 
> https://gitlab.com/qemu-project/qemu/-/issues/1198
> 
> Would you mind sharing if there is already any existing backport, or please let
> me know if I can send the backport to the linux-stable?
> 
> There are many conflicts unless we backport the entire patchset, e.g.,: I
> choose 0x7f1a/0x7ecb for 32-bit/64-bit int_shadow in the smram.
> 
> --------------------------------
> 
> From 90f492c865a4b7ca6187a4fc9eebe451f3d6c17e Mon Sep 17 00:00:00 2001
> From: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Date: Fri, 26 Jan 2024 14:03:59 -0800
> Subject: [PATCH linux-5.15.y 1/1] KVM: x86: smm: preserve interrupt shadow in SMRAM
> 
> [ Upstream commit fb28875fd7da184079150295da7ee8d80a70917e ]
> 
> When #SMI is asserted, the CPU can be in interrupt shadow due to sti or
> mov ss.
> 
> It is not mandatory in  Intel/AMD prm to have the #SMI blocked during the
> shadow, and on top of that, since neither SVM nor VMX has true support
> for SMI window, waiting for one instruction would mean single stepping
> the guest.
> 
> Instead, allow #SMI in this case, but both reset the interrupt window and
> stash its value in SMRAM to restore it on exit from SMM.
> 
> This fixes rare failures seen mostly on windows guests on VMX, when #SMI
> falls on the sti instruction which mainfest in VM entry failure due
> to EFLAGS.IF not being set, but STI interrupt window still being set
> in the VMCS.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Message-Id: <20221025124741.228045-24-mlevitsk@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> 
> Backport fb28875fd7da184079150295da7ee8d80a70917e from a big patchset
> merge:
> 
> [PATCH RESEND v4 00/23] SMM emulation and interrupt shadow fixes
> https://lore.kernel.org/all/20221025124741.228045-1-mlevitsk@xxxxxxxxxx/
> 
> Since only the last patch is backported, there are many conflicts.
> 
> The core idea of the patch:
> 
> - Save the interruptibility before entering SMM.
> - Load the interruptibility after leaving SMM.
> 
> Although the real offsets in smram buffer are the same, the bugfix and the
> UEK5 use different offsets in the function calls. Here are some examples.
> 
> 32-bit:
>               bugfix      UEK6

Apologies for my fault that I should use "bugfix" and "5.15.y" in the
table.

I may correct them if I need to send this backport to stable kernels.

So far just to confirm if there is already a backport from Maxim or Paolo
but just never get the chance to send out.

Thank you very much and apologies for the fault again!

Dongli Zhang

> smbase     -> 0xFEF8  -> 0x7ef8
> cr4        -> 0xFF14  -> 0x7f14
> int_shadow -> 0xFF1A  ->  n/a
> eip        -> 0xFFF0  -> 0x7ff0
> cr0        -> 0xFFFC  -> 0x7ffc
> 
> 64-bit:
>               bugfix      UEK6
> int_shadow -> 0xFECB  ->  n/a
> efer       -> 0xFEd0  -> 0x7ed0
> smbase     -> 0xFF00  -> 0x7f00
> cr4        -> 0xFF48  -> 0x7f48
> cr0        -> 0xFF58  -> 0x7f58
> rip        -> 0xFF78  -> 0x7f78
> 
> Therefore, we choose the below offsets for int_shadow:
> 
> 32-bit: int_shadow = 0x7f1a
> 64-bit: int_shadow = 0x7ecb
> 
> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
> ---
>  arch/x86/kvm/emulate.c | 15 +++++++++++++--
>  arch/x86/kvm/x86.c     |  6 ++++++
>  2 files changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 98b25a7..00df781b 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -2438,7 +2438,7 @@ static int rsm_load_state_32(struct x86_emulate_ctxt *ctxt,
>  	struct desc_ptr dt;
>  	u16 selector;
>  	u32 val, cr0, cr3, cr4;
> -	int i;
> +	int i, r;
> 
>  	cr0 =                      GET_SMSTATE(u32, smstate, 0x7ffc);
>  	cr3 =                      GET_SMSTATE(u32, smstate, 0x7ff8);
> @@ -2488,7 +2488,15 @@ static int rsm_load_state_32(struct x86_emulate_ctxt *ctxt,
> 
>  	ctxt->ops->set_smbase(ctxt, GET_SMSTATE(u32, smstate, 0x7ef8));
> 
> -	return rsm_enter_protected_mode(ctxt, cr0, cr3, cr4);
> +	r = rsm_enter_protected_mode(ctxt, cr0, cr3, cr4);
> +
> +	if (r != X86EMUL_CONTINUE)
> +		return r;
> +
> +	static_call(kvm_x86_set_interrupt_shadow)(ctxt->vcpu, 0);
> +	ctxt->interruptibility = GET_SMSTATE(u8, smstate, 0x7f1a);
> +
> +	return r;
>  }
> 
>  #ifdef CONFIG_X86_64
> @@ -2559,6 +2567,9 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
>  			return r;
>  	}
> 
> +	static_call(kvm_x86_set_interrupt_shadow)(ctxt->vcpu, 0);
> +	ctxt->interruptibility = GET_SMSTATE(u8, smstate, 0x7ecb);
> +
>  	return X86EMUL_CONTINUE;
>  }
>  #endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index aa6f700..6b30d40 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9400,6 +9400,8 @@ static void enter_smm_save_state_32(struct kvm_vcpu *vcpu, char *buf)
>  	/* revision id */
>  	put_smstate(u32, buf, 0x7efc, 0x00020000);
>  	put_smstate(u32, buf, 0x7ef8, vcpu->arch.smbase);
> +
> +	put_smstate(u8, buf, 0x7f1a, static_call(kvm_x86_get_interrupt_shadow)(vcpu));
>  }
> 
>  #ifdef CONFIG_X86_64
> @@ -9454,6 +9456,8 @@ static void enter_smm_save_state_64(struct kvm_vcpu *vcpu, char *buf)
> 
>  	for (i = 0; i < 6; i++)
>  		enter_smm_save_seg_64(vcpu, buf, i);
> +
> +	put_smstate(u8, buf, 0x7ecb, static_call(kvm_x86_get_interrupt_shadow)(vcpu));
>  }
>  #endif
> 
> @@ -9490,6 +9494,8 @@ static void enter_smm(struct kvm_vcpu *vcpu)
>  	kvm_set_rflags(vcpu, X86_EFLAGS_FIXED);
>  	kvm_rip_write(vcpu, 0x8000);
> 
> +	static_call(kvm_x86_set_interrupt_shadow)(vcpu, 0);
> +
>  	cr0 = vcpu->arch.cr0 & ~(X86_CR0_PE | X86_CR0_EM | X86_CR0_TS | X86_CR0_PG);
>  	static_call(kvm_x86_set_cr0)(vcpu, cr0);
>  	vcpu->arch.cr0 = cr0;
> --
> 1.8.3.1
> 
> --------------------------------
> 
> Thank you very much!
> 
> Dongli Zhang




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