[PATCH v2 1/8] x86/boot: Sanitise PKRU on boot

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

While the reset value of the register is 0, it might not be after kexec/etc.
If PKEY0.{WD,AD} have leaked in from an earlier context, construction of a PV
dom0 will explode.

Sequencing wise, this must come after setting CR4.PKE, and before we touch any
user mappings.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>

For sequencing, it could also come after setting XCR0.PKRU too, but then we'd
need to construct an empty XSAVE area to XRSTOR from, and that would be even
more horrible to arrange.
---
 xen/arch/x86/cpu/common.c             | 3 +++
 xen/arch/x86/include/asm/cpufeature.h | 1 +
 xen/arch/x86/setup.c                  | 2 +-
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 0412dbc915e5..fe92f29c2dc6 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -936,6 +936,9 @@ void cpu_init(void)
        write_debugreg(6, X86_DR6_DEFAULT);
        write_debugreg(7, X86_DR7_DEFAULT);
 
+       if (cpu_has_pku)
+               wrpkru(0);
+
        /*
         * If the platform is performing a Secure Launch via SKINIT, GIF is
         * clear to prevent external interrupts interfering with Secure
diff --git a/xen/arch/x86/include/asm/cpufeature.h 
b/xen/arch/x86/include/asm/cpufeature.h
index a3ad9ebee4e9..044cfd9f882d 100644
--- a/xen/arch/x86/include/asm/cpufeature.h
+++ b/xen/arch/x86/include/asm/cpufeature.h
@@ -109,6 +109,7 @@
 
 /* CPUID level 0x00000007:0.ecx */
 #define cpu_has_avx512_vbmi     boot_cpu_has(X86_FEATURE_AVX512_VBMI)
+#define cpu_has_pku             boot_cpu_has(X86_FEATURE_PKU)
 #define cpu_has_avx512_vbmi2    boot_cpu_has(X86_FEATURE_AVX512_VBMI2)
 #define cpu_has_gfni            boot_cpu_has(X86_FEATURE_GFNI)
 #define cpu_has_vaes            boot_cpu_has(X86_FEATURE_VAES)
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 566422600d94..6deadcf74763 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1798,7 +1798,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
     if ( boot_cpu_has(X86_FEATURE_FSGSBASE) )
         set_in_cr4(X86_CR4_FSGSBASE);
 
-    if ( boot_cpu_has(X86_FEATURE_PKU) )
+    if ( cpu_has_pku )
         set_in_cr4(X86_CR4_PKE);
 
     if ( opt_invpcid && cpu_has_invpcid )
-- 
2.11.0