Re: [PATCH v5 07/12] x86/traps: Add #VE support for TDX guest

Borislav Petkov
2021-08-24T10:17:00Z

On Wed, Aug 04, 2021 at 11:13:24AM -0700, Kuppuswamy Sathyanarayanan wrote:
> If a guest kernel action which would normally cause a #VE occurs in the
> interrupt-disabled region before TDGETVEINFO, a #DF is delivered to the
> guest which will result in an oops (and should eventually be a panic, as
> we would like to set panic_on_oops to 1 for TDX guests).

Who's "we"?

Please use passive voice in your commit message and comments: no "we"
or "I", etc. Personal pronouns are ambiguous in text, especially with
so many parties/companies/etc developing the kernel so let's avoid them.

Audit all your patchsets pls.

> Add basic infrastructure to handle any #VE which occurs in the kernel or
> userspace.  Later patches will add handling for specific #VE scenarios.
>
> Convert unhandled #VE's (everything, until later in this series) so that
> they appear just like a #GP by calling ve_raise_fault() directly.
> ve_raise_fault() is similar to #GP handler and is responsible for
> sending SIGSEGV to userspace and cpu die and notifying debuggers and

In all your text:

s/cpu/CPU/g

Audit all your patchsets pls.

> @@ -53,6 +67,11 @@ u64 __tdx_module_call(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
> u64 __tdx_hypercall(u64 type, u64 fn, u64 r12, u64 r13, u64 r14,
> u64 r15, struct tdx_hypercall_output *out);
>
> +unsigned long tdg_get_ve_info(struct ve_info *ve);
> +
> +int tdg_handle_virtualization_exception(struct pt_regs *regs,

There's that "tdg" prefix again. Please fix all your patchsets.

> + struct ve_info *ve);
> +
> #else
>
> static inline void tdx_early_init(void) { };
> diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
> index df0fa695bb09..a5eaae8e6c44 100644
> --- a/arch/x86/kernel/idt.c
> +++ b/arch/x86/kernel/idt.c
> @@ -68,6 +68,9 @@ static const __initconst struct idt_data early_idts[] = {
> */
> INTG(X86_TRAP_PF, asm_exc_page_fault),
> #endif
> +#ifdef CONFIG_INTEL_TDX_GUEST
> + INTG(X86_TRAP_VE, asm_exc_virtualization_exception),
> +#endif
> };
>
> /*
> @@ -91,6 +94,9 @@ static const __initconst struct idt_data def_idts[] = {
> INTG(X86_TRAP_MF, asm_exc_coprocessor_error),
> INTG(X86_TRAP_AC, asm_exc_alignment_check),
> INTG(X86_TRAP_XF, asm_exc_simd_coprocessor_error),
> +#ifdef CONFIG_INTEL_TDX_GUEST
> + INTG(X86_TRAP_VE, asm_exc_virtualization_exception),
> +#endif
>
> #ifdef CONFIG_X86_32
> TSKG(X86_TRAP_DF, GDT_ENTRY_DOUBLEFAULT_TSS),
> diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> index 3973e81751ba..6169f9c740b2 100644
> --- a/arch/x86/kernel/tdx.c
> +++ b/arch/x86/kernel/tdx.c
> @@ -10,6 +10,7 @@
>
> /* TDX Module call Leaf IDs */
> #define TDINFO 1
> +#define TDGETVEINFO 3
>
> static struct {
> unsigned int gpa_width;
> @@ -75,6 +76,41 @@ static void tdg_get_info(void)
> td_info.attributes = out.rdx;
> }
>
> +unsigned long tdg_get_ve_info(struct ve_info *ve)
> +{
> + u64 ret;
> + struct tdx_module_output out = {0};

The tip-tree preferred ordering of variable declarations at the
beginning of a function is reverse fir tree order::

struct long_struct_name *descriptive_name;
unsigned long foo, bar;
unsigned int tmp;
int ret;

The above is faster to parse than the reverse ordering::

int ret;
unsigned int tmp;
unsigned long foo, bar;
struct long_struct_name *descriptive_name;

And even more so than random ordering::

unsigned long foo, bar;
int ret;
struct long_struct_name *descriptive_name;
unsigned int tmp;

> +
> + /*
> + * NMIs and machine checks are suppressed. Before this point any
> + * #VE is fatal. After this point (TDGETVEINFO call), NMIs and
> + * additional #VEs are permitted (but we don't expect them to
> + * happen unless you panic).
> + */
> + ret = __tdx_module_call(TDGETVEINFO, 0, 0, 0, 0, &out);
> +
> + ve->exit_reason = out.rcx;
> + ve->exit_qual = out.rdx;
> + ve->gla = out.r8;
> + ve->gpa = out.r9;
> + ve->instr_len = out.r10 & UINT_MAX;
> + ve->instr_info = out.r10 >> 32;
> +
> + return ret;
> +}
> +
> +int tdg_handle_virtualization_exception(struct pt_regs *regs,
> + struct ve_info *ve)
> +{
> + /*
> + * TODO: Add handler support for various #VE exit
> + * reasons. It will be added by other patches in
> + * the series.
> + */

That comment needs to go.

> + pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
> + return -EFAULT;
> +}
> +
> void __init tdx_early_init(void)
> {
> if (!cpuid_has_tdx_guest())
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index a58800973aed..be56f0281cb5 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -61,6 +61,7 @@
> #include <asm/insn.h>
> #include <asm/insn-eval.h>
> #include <asm/vdso.h>
> +#include <asm/tdx.h>
>
> #ifdef CONFIG_X86_64
> #include <asm/x86_init.h>
> @@ -1140,6 +1141,74 @@ DEFINE_IDTENTRY(exc_device_not_available)
> }
> }
>
> +#ifdef CONFIG_INTEL_TDX_GUEST
> +#define VEFSTR "VE fault"
> +static void ve_raise_fault(struct pt_regs *regs, long error_code)
> +{
> + struct task_struct *tsk = current;
> +
> + if (user_mode(regs)) {
> + tsk->thread.error_code = error_code;
> + tsk->thread.trap_nr = X86_TRAP_VE;
> +
> + /*
> + * Not fixing up VDSO exceptions similar to #GP handler
> + * because we don't expect the VDSO to trigger #VE.
> + */
> + show_signal(tsk, SIGSEGV, "", VEFSTR, regs, error_code);
> + force_sig(SIGSEGV);
> + return;
> + }
> +
> + if (fixup_exception(regs, X86_TRAP_VE, error_code, 0))

There are exception table entries which can trigger a #VE?

> + return;
> +
> + tsk->thread.error_code = error_code;
> + tsk->thread.trap_nr = X86_TRAP_VE;
> +
> + /*
> + * To be potentially processing a kprobe fault and to trust the result
> + * from kprobe_running(), we have to be non-preemptible.
> + */
> + if (!preemptible() &&
> + kprobe_running() &&
> + kprobe_fault_handler(regs, X86_TRAP_VE))
> + return;
> +
> + notify_die(DIE_GPF, VEFSTR, regs, error_code, X86_TRAP_VE, SIGSEGV);

Other handlers check that retval.

--
Regards/Gruss,
Boris.