From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from foss.arm.com (foss.arm.com [217.140.110.172])
 by mx.groups.io with SMTP id smtpd.web12.655.1591812461168519623
 for <devel@edk2.groups.io>;
 Wed, 10 Jun 2020 11:07:41 -0700
Authentication-Results: mx.groups.io;
 dkim=missing; spf=pass (domain: arm.com, ip: 217.140.110.172, mailfrom: ard.biesheuvel@arm.com)
Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14])
	by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A61BC1FB;
	Wed, 10 Jun 2020 11:07:39 -0700 (PDT)
Received: from [192.168.1.69] (unknown [172.31.20.19])
	by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E6CCE3F66F;
	Wed, 10 Jun 2020 11:07:38 -0700 (PDT)
Subject: Re: [PATCH] ArmPkg/ArmExceptionLib: use static buffer for sp_el0
To: Heyi Guo <guoheyi@linux.alibaba.com>, devel@edk2.groups.io
Cc: yitian.ly@alibaba-inc.com, Leif Lindholm <leif@nuviainc.com>
References: <1591665990-15342-1-git-send-email-guoheyi@linux.alibaba.com>
From: "Ard Biesheuvel" <ard.biesheuvel@arm.com>
Message-ID: <679afd8a-bb5a-9ae2-0266-3235ed227bfd@arm.com>
Date: Wed, 10 Jun 2020 20:07:36 +0200
User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:68.0) Gecko/20100101
 Thunderbird/68.9.0
MIME-Version: 1.0
In-Reply-To: <1591665990-15342-1-git-send-email-guoheyi@linux.alibaba.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit

On 6/9/20 3:26 AM, Heyi Guo wrote:
> The exception library is also used in DxeMain before memory services
> are available, and AllocatePages() will fail in this case and cause
> sp_el0 remains 0. Then if any exception occurs before CpuDxe driver is
> loaded, a recursive exception will be trigged by page translation
> fault for sp = 0 - 0x130.
> 
> Use static buffer instead to fix this issue.
> 
> Signed-off-by: Heyi Guo <guoheyi@linux.alibaba.com>
> 

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

Merged as #679

> ---
> 
> Cc: Leif Lindholm <leif@nuviainc.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> ---
>   ArmPkg/Library/ArmExceptionLib/AArch64/AArch64Exception.c | 14 ++++++--------
>   1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/ArmPkg/Library/ArmExceptionLib/AArch64/AArch64Exception.c b/ArmPkg/Library/ArmExceptionLib/AArch64/AArch64Exception.c
> index be1cdcf..1e2aeaa 100644
> --- a/ArmPkg/Library/ArmExceptionLib/AArch64/AArch64Exception.c
> +++ b/ArmPkg/Library/ArmExceptionLib/AArch64/AArch64Exception.c
> @@ -19,7 +19,8 @@ EFI_EXCEPTION_CALLBACK  gDebuggerExceptionHandlers[MAX_AARCH64_EXCEPTION + 1] =
>   PHYSICAL_ADDRESS        gExceptionVectorAlignmentMask = ARM_VECTOR_TABLE_ALIGNMENT;
>   UINTN                   gDebuggerNoHandlerValue = 0; // todo: define for AArch64
>   
> -#define EL0_STACK_PAGES   2
> +#define EL0_STACK_SIZE  EFI_PAGES_TO_SIZE(2)
> +STATIC UINTN mNewStackBase[EL0_STACK_SIZE / sizeof (UINTN)];
>   
>   VOID
>   RegisterEl0Stack (
> @@ -31,14 +32,11 @@ RETURN_STATUS ArchVectorConfig(
>     )
>   {
>     UINTN             HcrReg;
> -  UINT8             *Stack;
>   
> -  Stack = AllocatePages (EL0_STACK_PAGES);
> -  if (Stack == NULL) {
> -    return RETURN_OUT_OF_RESOURCES;
> -  }
> -
> -  RegisterEl0Stack ((UINT8 *)Stack + EFI_PAGES_TO_SIZE (EL0_STACK_PAGES));
> +  // Round down sp by 16 bytes alignment
> +  RegisterEl0Stack (
> +    (VOID *) (((UINTN) mNewStackBase + EL0_STACK_SIZE) & ~0xFUL)
> +    );
>   
>     if (ArmReadCurrentEL() == AARCH64_EL2) {
>       HcrReg = ArmReadHcr();
>