Re: [PATCH] OvmfPkg: fix dynamic default for oprom verification policy PCD without SB

[Jordan Justen <jordan.l.justen@intel.com>]

On 2017-10-17 15:23:21, Laszlo Ersek wrote:
> I missed the following, both while reviewing and while testing commit
> 6041ac65ae87 ("OvmfPkg/PlatformPei: DENY_EXECUTE_ON_SECURITY_VIOLATION
> when SEV is active", 2017-10-05):
> 
> If "-D SECURE_BOOT_ENABLE" is not passed on the "build" command line, then
> OVMF has no dynamic default at all for
> "PcdOptionRomImageVerificationPolicy". This means that the PcdSet32S()
> call added in the subject commit doesn't even compile:
> 
> > OvmfPkg/PlatformPei/AmdSev.c: In function 'AmdSevInitialize':
> > OvmfPkg/PlatformPei/AmdSev.c:67:3: error: implicit declaration of
> > function '_PCD_SET_MODE_32_S_PcdOptionRomImageVerificationPolicy'
> > [-Werror=implicit-function-declaration]
> >    PcdStatus = PcdSet32S (PcdOptionRomImageVerificationPolicy, 0x4);
> >    ^
> > cc1: all warnings being treated as errors
> 
> There are three ways to fix the error:
> 
> (1) Make the current, SB-only, 0x00 dynamic default unconditional.

Maybe you should say something like, "As implemented in this patch..."
for item (1). Or, just drop (2) and (3) entirely in the commit
message. I'll leave that up to you.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

> 
>     This is the simplest approach, and it reflects the intent of original
>     commit 1fea9ddb4e3f ("OvmfPkg: execute option ROM images regardless of
>     Secure Boot", 2016-01-07). Without SECURE_BOOT_ENABLE,
>     "SecurityPkg/Library/DxeImageVerificationLib" is not used anyway, so
>     the PCD is never read.
> 
> (2) Add an !else branch that explicitly sets the SecurityPkg.dec default
>     (0x04) as dynamic default, if SECURE_BOOT_ENABLE is FALSE.
> 
>     This looks awkward because it explicitly sets a dynamic default that
>     is then never read.
> 
> (3) Set the SecurityPkg.dec default (0x04) as unconditional dynamic
>     default, and invert the logic in AmdSevInitialize()
>     [OvmfPkg/PlatformPei/AmdSev.c] -- set the PCD to 0x00 if SEV is
>     disabled; don't touch it otherwise.
> 
>     I think this sends the wrong message -- for the time being anyway, SEV
>     is the exception, not the rule. We shouldn't rely on the PCD getting
>     its most commonly used value in a function called AmdSevInitialize().
> 
> This issue was caught and reported by Gerd Hoffmann <kraxel@redhat.com>'s
> Jenkins CI.
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Fixes: 6041ac65ae879389f3ab5c0699f916d3e71c97fe
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
> 
> Notes:
>     Repo:   https://github.com/lersek/edk2.git
>     Branch: oprom_policy_build_fix
> 
>  OvmfPkg/OvmfPkgIa32.dsc    | 3 ---
>  OvmfPkg/OvmfPkgIa32X64.dsc | 3 ---
>  OvmfPkg/OvmfPkgX64.dsc     | 3 ---
>  3 files changed, 9 deletions(-)
> 
> diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
> index 7fb557b7c9cd..c2f534fdbf3b 100644
> --- a/OvmfPkg/OvmfPkgIa32.dsc
> +++ b/OvmfPkg/OvmfPkgIa32.dsc
> @@ -540,10 +540,7 @@ [PcdsDynamicDefault]
>    gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmApSyncTimeout|100000
>  !endif
>  
> -!if $(SECURE_BOOT_ENABLE) == TRUE
>    gEfiSecurityPkgTokenSpaceGuid.PcdOptionRomImageVerificationPolicy|0x00
> -!endif
> -
>  
>  ################################################################################
>  #
> diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
> index 4bcbddb95768..9f300a2e6f32 100644
> --- a/OvmfPkg/OvmfPkgIa32X64.dsc
> +++ b/OvmfPkg/OvmfPkgIa32X64.dsc
> @@ -548,10 +548,7 @@ [PcdsDynamicDefault]
>    gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmApSyncTimeout|100000
>  !endif
>  
> -!if $(SECURE_BOOT_ENABLE) == TRUE
>    gEfiSecurityPkgTokenSpaceGuid.PcdOptionRomImageVerificationPolicy|0x00
> -!endif
> -
>  
>  ################################################################################
>  #
> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
> index e52a3bd4db9b..1ffcf37f8b92 100644
> --- a/OvmfPkg/OvmfPkgX64.dsc
> +++ b/OvmfPkg/OvmfPkgX64.dsc
> @@ -547,10 +547,7 @@ [PcdsDynamicDefault]
>    gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmApSyncTimeout|100000
>  !endif
>  
> -!if $(SECURE_BOOT_ENABLE) == TRUE
>    gEfiSecurityPkgTokenSpaceGuid.PcdOptionRomImageVerificationPolicy|0x00
> -!endif
> -
>  
>  ################################################################################
>  #
> -- 
> 2.14.1.3.gb7cf6e02401b
>