On 14.02.2022 17:39, Andrew Cooper wrote:
> On 14/02/2022 13:35, Andrew Cooper wrote:
>> On 14/02/2022 13:10, Jan Beulich wrote:
>>> On 14.02.2022 13:56, Andrew Cooper wrote:
>>>> --- a/xen/arch/x86/hvm/hvm.c
>>>> +++ b/xen/arch/x86/hvm/hvm.c
>>>> @@ -88,7 +88,7 @@ unsigned int opt_hvm_debug_level __read_mostly;
>>>> integer_param("hvm_debug", opt_hvm_debug_level);
>>>> #endif
>>>>
>>>> -struct hvm_function_table hvm_funcs __read_mostly;
>>>> +struct hvm_function_table __ro_after_init hvm_funcs;
>>> Strictly speaking this is an unrelated change. I'm fine with it living here,
>>> but half a sentence would be nice in the description.
>> I could split it out, but we could probably make 200 patches of
>> "sprinkle some __ro_after_init around, now that it exists".
>>
>>>> --- a/xen/arch/x86/hvm/svm/svm.c
>>>> +++ b/xen/arch/x86/hvm/svm/svm.c
>>>> @@ -2513,7 +2513,7 @@ static void cf_check svm_set_reg(struct vcpu *v,
>>>> unsigned int reg, uint64_t val)
>>>> }
>>>> }
>>>>
>>>> -static struct hvm_function_table __initdata svm_function_table = {
>>>> +static struct hvm_function_table __initdata_cf_clobber svm_function_table
>>>> = {
>>>> .name = "SVM",
>>>> .cpu_up_prepare = svm_cpu_up_prepare,
>>>> .cpu_dead = svm_cpu_dead,
>>>> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
>>>> index 41db538a9e3d..758df3321884 100644
>>>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>>>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>>>> @@ -2473,7 +2473,7 @@ static void cf_check vmx_set_reg(struct vcpu *v,
>>>> unsigned int reg, uint64_t val)
>>>> vmx_vmcs_exit(v);
>>>> }
>>>>
>>>> -static struct hvm_function_table __initdata vmx_function_table = {
>>>> +static struct hvm_function_table __initdata_cf_clobber vmx_function_table
>>>> = {
>>>> .name = "VMX",
>>>> .cpu_up_prepare = vmx_cpu_up_prepare,
>>>> .cpu_dead = vmx_cpu_dead,
>>> While I'd like to re-raise my concern regarding the non-pointer fields
>>> in these structure instances (just consider a sequence of enough bool
>>> bitfields, which effectively can express any value, including ones
>>> which would appear like pointers into .text), since for now all is okay
>>> afaict:
>>> Reviewed-by: Jan Beulich <jbeul...@suse.com>
>> I should probably put something in the commit message too. It is a
>> theoretical risk, but not (IMO) a practical one.
>
> Updated commit message:
>
> x86/hvm: Use __initdata_cf_clobber for hvm_funcs
>
> Now that all calls through hvm_funcs are fully altcall'd, harden all the svm
> and vmx function pointer targets. This drops 106 endbr64 instructions.
>
> Clobbering does come with a theoretical risk. The non-pointer fields of
> {svm,vmx}_function_table can in theory happen to form a bit pattern
> matching a
> pointer into .text at a legal endbr64 instruction, but this is expected
> to be
> implausible for anything liable to pass code review.
>
> While at it, move hvm_funcs into __ro_after_init now that this exists.
SGTM, thanks.
Jan
