Messages in this thread Patch in this message | | | From | Kuppuswamy Sathyanarayanan <> | Subject | [PATCH v8 06/11] x86/traps: Add #VE support for TDX guest | Date | Mon, 4 Oct 2021 19:52:00 -0700 |
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From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Virtualization Exceptions (#VE) are delivered to TDX guests due to specific guest actions which may happen in either user space or the kernel:
* Specific instructions (WBINVD, for example) * Specific MSR accesses * Specific CPUID leaf accesses * Access to TD-shared memory, which includes MMIO
In the settings that Linux will run in, virtual exceptions are never generated on accesses to normal, TD-private memory that has been accepted.
The entry paths do not access TD-shared memory, MMIO regions or use those specific MSRs, instructions, CPUID leaves that might generate #VE. In addition, all interrupts including NMIs are blocked by the hardware starting with #VE delivery until TDGETVEINFO is called. This eliminates the chance of a #VE during the syscall gap or paranoid entry paths and simplifies #VE handling.
After TDGETVEINFO #VE could happen in theory (e.g. through an NMI), but it is expected not to happen because TDX expects NMIs not to trigger #VEs. Another case where they could happen is if the #VE exception panics, but in this case there are no guarantees on anything anyways.
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 it is expected panic_on_oops is set to 1 for TDX guests).
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 other die chain users.
Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Andi Kleen <ak@linux.intel.com> Reviewed-by: Tony Luck <tony.luck@intel.com> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> ---
Changes since v7: * None
Changes since v6: * None
Changes since v5: * Fixed "We" usage in commit log and replaced cpu -> CPU. * Renamed "tdg_" prefix with "tdx_". * Removed TODO comment in tdg_handle_virtualization_exception() as per Boris review comments. * Added comments for ve_raise_fault().
Changes since v4: * Since ve_raise_fault() is used only by TDX code, moved it within #ifdef CONFIG_INTEL_TDX_GUEST.
Changes since v3: * None
arch/x86/include/asm/idtentry.h | 4 ++ arch/x86/include/asm/tdx.h | 19 ++++++++ arch/x86/kernel/idt.c | 6 +++ arch/x86/kernel/tdx.c | 33 ++++++++++++++ arch/x86/kernel/traps.c | 77 +++++++++++++++++++++++++++++++++ 5 files changed, 139 insertions(+)
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h index 1345088e9902..8ccc81d653b3 100644 --- a/arch/x86/include/asm/idtentry.h +++ b/arch/x86/include/asm/idtentry.h @@ -625,6 +625,10 @@ DECLARE_IDTENTRY_XENCB(X86_TRAP_OTHER, exc_xen_hypervisor_callback); DECLARE_IDTENTRY_RAW(X86_TRAP_OTHER, exc_xen_unknown_trap); #endif +#ifdef CONFIG_INTEL_TDX_GUEST +DECLARE_IDTENTRY(X86_TRAP_VE, exc_virtualization_exception); +#endif + /* Device interrupts common/spurious */ DECLARE_IDTENTRY_IRQ(X86_TRAP_OTHER, common_interrupt); #ifdef CONFIG_X86_LOCAL_APIC diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h index 8d83a719b90b..458a564dd4c2 100644 --- a/arch/x86/include/asm/tdx.h +++ b/arch/x86/include/asm/tdx.h @@ -39,6 +39,20 @@ struct tdx_hypercall_output { u64 r15; }; +/* + * Used by #VE exception handler to gather the #VE exception + * info from the TDX module. This is software only structure + * and not related to TDX module/VMM. + */ +struct ve_info { + u64 exit_reason; + u64 exit_qual; + u64 gla; /* Guest Linear (virtual) Address */ + u64 gpa; /* Guest Physical (virtual) Address */ + u32 instr_len; + u32 instr_info; +}; + #ifdef CONFIG_INTEL_TDX_GUEST extern u64 is_tdx_guest; @@ -52,6 +66,11 @@ 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 tdx_get_ve_info(struct ve_info *ve); + +int tdx_handle_virtualization_exception(struct pt_regs *regs, + struct ve_info *ve); + #else #define is_tdx_guest 0ULL 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 d5fc2904facf..f7885c777a09 100644 --- a/arch/x86/kernel/tdx.c +++ b/arch/x86/kernel/tdx.c @@ -6,6 +6,9 @@ #include <asm/tdx.h> +/* TDX Module call Leaf IDs */ +#define TDGETVEINFO 3 + /* * Allocate it in the data region to avoid zeroing it during * BSS initialization. It is mainly used in cc_platform_has() @@ -50,6 +53,36 @@ static inline u64 _tdx_hypercall(u64 fn, u64 r12, u64 r13, u64 r14, return out->r10; } +unsigned long tdx_get_ve_info(struct ve_info *ve) +{ + struct tdx_module_output out = {0}; + u64 ret; + + /* + * 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 it is expected not to + * happen unless kernel panics). + */ + 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 tdx_handle_virtualization_exception(struct pt_regs *regs, + struct ve_info *ve) +{ + pr_warn("Unexpected #VE: %lld\n", ve->exit_reason); + return -EFAULT; +} + void __init tdx_early_init(void) { is_tdx_guest_init(); diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index a58800973aed..152d1d3b9dc8 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 +1141,82 @@ 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 it is expected that VDSO doesn't trigger #VE. + */ + show_signal(tsk, SIGSEGV, "", VEFSTR, regs, error_code); + force_sig(SIGSEGV); + return; + } + + /* + * Attempt to recover from #VE exception failure without + * triggering OOPS (useful for MSR read/write failures) + */ + if (fixup_exception(regs, X86_TRAP_VE, error_code, 0)) + 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(), it should be non-preemptible. + */ + if (!preemptible() && + kprobe_running() && + kprobe_fault_handler(regs, X86_TRAP_VE)) + return; + + /* Notify about #VE handling failure, useful for debugger hooks */ + if (notify_die(DIE_GPF, VEFSTR, regs, error_code, + X86_TRAP_VE, SIGSEGV) == NOTIFY_STOP) + return; + + /* Trigger OOPS and panic */ + die_addr(VEFSTR, regs, error_code, 0); +} + +DEFINE_IDTENTRY(exc_virtualization_exception) +{ + struct ve_info ve; + int ret; + + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); + + /* + * NMIs/Machine-checks/Interrupts will be in a disabled state + * till TDGETVEINFO TDCALL is executed. This prevents #VE + * nesting issue. + */ + ret = tdx_get_ve_info(&ve); + + cond_local_irq_enable(regs); + + if (!ret) + ret = tdx_handle_virtualization_exception(regs, &ve); + /* + * If tdx_handle_virtualization_exception() could not process + * it successfully, treat it as #GP(0) and handle it. + */ + if (ret) + ve_raise_fault(regs, 0); + + cond_local_irq_disable(regs); +} +#endif + #ifdef CONFIG_X86_32 DEFINE_IDTENTRY_SW(iret_error) { -- 2.25.1
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