Re: [PATCH v13 26/35] x86/fred: FRED entry/exit and dispatch code
From: Andrew Cooper <hidden>
Date: 2023-12-05 12:25:34
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On 05/12/2023 10:50 am, Xin Li wrote:
quoted hunk ↗ jump to hunk
diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c new file mode 100644 index 000000000000..215883e90f94 --- /dev/null +++ b/arch/x86/entry/entry_fred.c@@ -0,0 +1,230 @@... +static noinstr void fred_intx(struct pt_regs *regs) +{ + switch (regs->fred_ss.vector) { + /* INT0 */
INTO (for overflow), not INT-zero. However...
+ case X86_TRAP_OF: + exc_overflow(regs); + return; + + /* INT3 */ + case X86_TRAP_BP: + exc_int3(regs); + return;
... neither OF nor BP will ever enter fred_intx() because they're type SWEXC not SWINT. SWINT is strictly the INT $imm8 instruction.
...
+static noinstr void fred_extint(struct pt_regs *regs)
+{
+ unsigned int vector = regs->fred_ss.vector;
+
+ if (WARN_ON_ONCE(vector < FIRST_EXTERNAL_VECTOR))
+ return;
+
+ if (likely(vector >= FIRST_SYSTEM_VECTOR)) {
+ irqentry_state_t state = irqentry_enter(regs);
+
+ instrumentation_begin();
+ sysvec_table[vector - FIRST_SYSTEM_VECTOR](regs);array_index_mask_nospec() This is easy for an attacker to abuse, to install non-function-pointer targets into the indirect predictor.
+ instrumentation_end();
+ irqentry_exit(regs, state);
+ } else {
+ common_interrupt(regs, vector);
+ }
+}
+
+static noinstr void fred_exception(struct pt_regs *regs, unsigned long error_code)
+{
+ /* Optimize for #PF. That's the only exception which matters performance wise */
+ if (likely(regs->fred_ss.vector == X86_TRAP_PF)) {
+ exc_page_fault(regs, error_code);
+ return;
+ }
+
+ switch (regs->fred_ss.vector) {
+ case X86_TRAP_DE: return exc_divide_error(regs);
+ case X86_TRAP_DB: return fred_exc_debug(regs);
+ case X86_TRAP_BP: return exc_int3(regs);
+ case X86_TRAP_OF: return exc_overflow(regs);Depending on what you want to do with BP/OF vs fred_intx(), this may need adjusting. If you are cross-checking type and vector, then these should be rejected for not being of type HWEXC.
+ case X86_TRAP_BR: return exc_bounds(regs); + case X86_TRAP_UD: return exc_invalid_op(regs); + case X86_TRAP_NM: return exc_device_not_available(regs); + case X86_TRAP_DF: return exc_double_fault(regs, error_code); + case X86_TRAP_TS: return exc_invalid_tss(regs, error_code); + case X86_TRAP_NP: return exc_segment_not_present(regs, error_code); + case X86_TRAP_SS: return exc_stack_segment(regs, error_code); + case X86_TRAP_GP: return exc_general_protection(regs, error_code); + case X86_TRAP_MF: return exc_coprocessor_error(regs); + case X86_TRAP_AC: return exc_alignment_check(regs, error_code); + case X86_TRAP_XF: return exc_simd_coprocessor_error(regs); + +#ifdef CONFIG_X86_MCE + case X86_TRAP_MC: return fred_exc_machine_check(regs); +#endif +#ifdef CONFIG_INTEL_TDX_GUEST + case X86_TRAP_VE: return exc_virtualization_exception(regs); +#endif +#ifdef CONFIG_X86_KERNEL_IBT
CONFIG_X86_CET Userspace can use CET even if the kernel isn't compiled with IBT, so this exception needs handling.
+ case X86_TRAP_CP: return exc_control_protection(regs, error_code);
+#endif
+ default: return fred_bad_type(regs, error_code);
+ }
+}
+
+__visible noinstr void fred_entry_from_user(struct pt_regs *regs)
+{
+ unsigned long error_code = regs->orig_ax;
+
+ /* Invalidate orig_ax so that syscall_get_nr() works correctly */
+ regs->orig_ax = -1;
+
+ switch (regs->fred_ss.type) {
+ case EVENT_TYPE_EXTINT:
+ return fred_extint(regs);
+ case EVENT_TYPE_NMI:
+ return fred_exc_nmi(regs);
+ case EVENT_TYPE_SWINT:
+ return fred_intx(regs);
+ case EVENT_TYPE_HWEXC:
+ case EVENT_TYPE_SWEXC:
+ case EVENT_TYPE_PRIV_SWEXC:
+ return fred_exception(regs, error_code);PRIV_SWEXC should have it's own function and not fall into fred_exception(). It is strictly only the ICEBP (INT1) instruction at the moment, so should fall into bad_type() for any vector other than X86_TRAP_DB.
+ case EVENT_TYPE_OTHER: + return fred_other(regs); + default: + return fred_bad_type(regs, error_code); + } +}
~Andrew