| Message ID | 20231221140239.4349-3-weijiang.yang@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Enable CET Virtualization | expand |
On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote: > Remove XFEATURE_CET_USER entry from dependency array as the entry doesn't > reflect true dependency between CET features and the user xstate bit. > Enable the bit in fpu_kernel_cfg.max_features when either SHSTK or IBT is > available. > > Both user mode shadow stack and indirect branch tracking features depend > on XFEATURE_CET_USER bit in XSS to automatically save/restore user mode > xstate registers, i.e., IA32_U_CET and IA32_PL3_SSP whenever necessary. > > Note, the issue, i.e., CPUID only enumerates IBT but no SHSTK is resulted > from CET KVM series which synthesizes guest CPUIDs based on userspace > settings,in real world the case is rare. In other words, the existing > dependency check is correct when only user mode SHSTK is available. > > Signed-off-by: Yang Weijiang <weijiang.yang@intel.com> > Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com> > Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com> > --- > arch/x86/kernel/fpu/xstate.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c > index 07911532b108..f6b98693da59 100644 > --- a/arch/x86/kernel/fpu/xstate.c > +++ b/arch/x86/kernel/fpu/xstate.c > @@ -73,7 +73,6 @@ static unsigned short xsave_cpuid_features[] __initdata = { > [XFEATURE_PT_UNIMPLEMENTED_SO_FAR] = X86_FEATURE_INTEL_PT, > [XFEATURE_PKRU] = X86_FEATURE_OSPKE, > [XFEATURE_PASID] = X86_FEATURE_ENQCMD, > - [XFEATURE_CET_USER] = X86_FEATURE_SHSTK, > [XFEATURE_XTILE_CFG] = X86_FEATURE_AMX_TILE, > [XFEATURE_XTILE_DATA] = X86_FEATURE_AMX_TILE, > }; > @@ -798,6 +797,14 @@ void __init fpu__init_system_xstate(unsigned int legacy_size) > fpu_kernel_cfg.max_features &= ~BIT_ULL(i); > } > > + /* > + * CET user mode xstate bit has been cleared by above sanity check. > + * Now pick it up if either SHSTK or IBT is available. Either feature > + * depends on the xstate bit to save/restore user mode states. > + */ > + if (boot_cpu_has(X86_FEATURE_SHSTK) || boot_cpu_has(X86_FEATURE_IBT)) > + fpu_kernel_cfg.max_features |= BIT_ULL(XFEATURE_CET_USER); > + I am still not convinced that this is not a workaround for a bug in the sanity check code, and I don't really like this, but whatever, as long as the code works, I don't intend to fight over this. Let it be. Best regards, Maxim Levitsky > if (!cpu_feature_enabled(X86_FEATURE_XFD)) > fpu_kernel_cfg.max_features &= ~XFEATURE_MASK_USER_DYNAMIC; >
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 07911532b108..f6b98693da59 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -73,7 +73,6 @@ static unsigned short xsave_cpuid_features[] __initdata = { [XFEATURE_PT_UNIMPLEMENTED_SO_FAR] = X86_FEATURE_INTEL_PT, [XFEATURE_PKRU] = X86_FEATURE_OSPKE, [XFEATURE_PASID] = X86_FEATURE_ENQCMD, - [XFEATURE_CET_USER] = X86_FEATURE_SHSTK, [XFEATURE_XTILE_CFG] = X86_FEATURE_AMX_TILE, [XFEATURE_XTILE_DATA] = X86_FEATURE_AMX_TILE, }; @@ -798,6 +797,14 @@ void __init fpu__init_system_xstate(unsigned int legacy_size) fpu_kernel_cfg.max_features &= ~BIT_ULL(i); } + /* + * CET user mode xstate bit has been cleared by above sanity check. + * Now pick it up if either SHSTK or IBT is available. Either feature + * depends on the xstate bit to save/restore user mode states. + */ + if (boot_cpu_has(X86_FEATURE_SHSTK) || boot_cpu_has(X86_FEATURE_IBT)) + fpu_kernel_cfg.max_features |= BIT_ULL(XFEATURE_CET_USER); + if (!cpu_feature_enabled(X86_FEATURE_XFD)) fpu_kernel_cfg.max_features &= ~XFEATURE_MASK_USER_DYNAMIC;