[RFC PATCH v3 21/32] x86/fred: FRED entry/exit and dispatch code

Xin Li
2023-02-24T07:29:11Z

The code to actually handle kernel and event entry/exit using
FRED. It is split up into two files thus:

- entry_64_fred.S contains the actual entrypoints and exit code, and
saves and restores registers.
- entry_fred.c contains the two-level event dispatch code for FRED.
The first-level dispatch is on the event type, and the second-level
is on the event vector.

Originally-by: Megha Dey <megha.dey@intel.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Co-developed-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---

Changes since v1:
* Initialize a FRED exception handler to fred_bad_event() instead of NULL
if no FRED handler defined for an exception vector (Peter Zijlstra).
* Push calling irqentry_{enter,exit}() and instrumentation_{begin,end}()
down into individual FRED exception handlers, instead of in the dispatch
framework (Peter Zijlstra).
---
arch/x86/entry/Makefile | 5 +-
arch/x86/entry/entry_64_fred.S | 55 ++++++++
arch/x86/entry/entry_fred.c | 232 ++++++++++++++++++++++++++++++++
arch/x86/include/asm/idtentry.h | 8 ++
4 files changed, 299 insertions(+), 1 deletion(-)
create mode 100644 arch/x86/entry/entry_64_fred.S
create mode 100644 arch/x86/entry/entry_fred.c

diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile
index ca2fe186994b..c93e7f5c2a06 100644
--- a/arch/x86/entry/Makefile
+++ b/arch/x86/entry/Makefile
@@ -18,6 +18,9 @@ obj-y += vdso/
obj-y += vsyscall/

obj-$(CONFIG_PREEMPTION) += thunk_$(BITS).o
+CFLAGS_entry_fred.o += -fno-stack-protector
+CFLAGS_REMOVE_entry_fred.o += -pg $(CC_FLAGS_FTRACE)
+obj-$(CONFIG_X86_FRED) += entry_64_fred.o entry_fred.o
+
obj-$(CONFIG_IA32_EMULATION) += entry_64_compat.o syscall_32.o
obj-$(CONFIG_X86_X32_ABI) += syscall_x32.o
-
diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S
new file mode 100644
index 000000000000..1fb765fd3871
--- /dev/null
+++ b/arch/x86/entry/entry_64_fred.S
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * arch/x86/entry/entry_64_fred.S
+ *
+ * The actual FRED entry points.
+ */
+#include <linux/linkage.h>
+#include <asm/errno.h>
+#include <asm/asm-offsets.h>
+#include <asm/fred.h>
+
+#include "calling.h"
+
+ .code64
+ .section ".noinstr.text", "ax"
+
+.macro FRED_ENTER
+ UNWIND_HINT_EMPTY
+ PUSH_AND_CLEAR_REGS
+ movq %rsp, %rdi /* %rdi -> pt_regs */
+.endm
+
+.macro FRED_EXIT
+ UNWIND_HINT_REGS
+ POP_REGS
+ addq $8,%rsp /* Drop error code */
+.endm
+
+/*
+ * The new RIP value that FRED event delivery establishes is
+ * IA32_FRED_CONFIG & ~FFFH for events that occur in ring 3.
+ * Thus the FRED ring 3 entry point must be 4K page aligned.
+ */
+ .align 4096
+
+SYM_CODE_START_NOALIGN(fred_entrypoint_user)
+ FRED_ENTER
+ call fred_entry_from_user
+SYM_INNER_LABEL(fred_exit_user, SYM_L_GLOBAL)
+ FRED_EXIT
+ ERETU
+SYM_CODE_END(fred_entrypoint_user)
+
+/*
+ * The new RIP value that FRED event delivery establishes is
+ * (IA32_FRED_CONFIG & ~FFFH) + 256 for events that occur in
+ * ring 0, i.e., fred_entrypoint_user + 256.
+ */
+ .org fred_entrypoint_user+256
+SYM_CODE_START_NOALIGN(fred_entrypoint_kernel)
+ FRED_ENTER
+ call fred_entry_from_kernel
+ FRED_EXIT
+ ERETS
+SYM_CODE_END(fred_entrypoint_kernel)
diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c
new file mode 100644
index 000000000000..8d3e144670d6
--- /dev/null
+++ b/arch/x86/entry/entry_fred.c
@@ -0,0 +1,232 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * arch/x86/entry/entry_fred.c
+ *
+ * This contains the dispatch functions called from the entry point
+ * assembly.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kdebug.h> /* oops_begin/end, ... */
+#include <linux/nospec.h>
+#include <asm/event-type.h>
+#include <asm/fred.h>
+#include <asm/idtentry.h>
+#include <asm/syscall.h>
+#include <asm/trapnr.h>
+#include <asm/traps.h>
+#include <asm/kdebug.h>
+
+/*
+ * Badness...
+ */
+static DEFINE_FRED_HANDLER(fred_bad_event)
+{
+ irqentry_state_t irq_state = irqentry_nmi_enter(regs);
+
+ instrumentation_begin();
+
+ /* Panic on events from a high stack level */
+ if (regs->current_stack_level > 0) {
+ pr_emerg("PANIC: invalid or fatal FRED event; event type %u "
+ "vector %u error 0x%lx aux 0x%lx at %04x:%016lx\n",
+ regs->type, regs->vector, regs->orig_ax,
+ fred_event_data(regs), regs->cs, regs->ip);
+ die("invalid or fatal FRED event", regs, regs->orig_ax);
+ panic("invalid or fatal FRED event");
+ } else {
+ unsigned long flags = oops_begin();
+ int sig = SIGKILL;
+
+ pr_alert("BUG: invalid or fatal FRED event; event type %u "
+ "vector %u error 0x%lx aux 0x%lx at %04x:%016lx\n",
+ regs->type, regs->vector, regs->orig_ax,
+ fred_event_data(regs), regs->cs, regs->ip);
+
+ if (__die("Invalid or fatal FRED event", regs, regs->orig_ax))
+ sig = 0;
+
+ oops_end(flags, regs, sig);
+ }
+
+ instrumentation_end();
+ irqentry_nmi_exit(regs, irq_state);
+}
+
+noinstr void fred_exc_double_fault(struct pt_regs *regs)
+{
+ exc_double_fault(regs, regs->orig_ax);
+}
+
+/*
+ * Exception entry
+ */
+static DEFINE_FRED_HANDLER(fred_exception)
+{
+ /*
+ * Exceptions that cannot happen on FRED h/w are set to fred_bad_event().
+ */
+ static const fred_handler exception_handlers[NUM_EXCEPTION_VECTORS] = {
+ [X86_TRAP_DE] = exc_divide_error,
+ [X86_TRAP_DB] = fred_exc_debug,
+ [X86_TRAP_NMI] = fred_bad_event, /* A separate event type, not handled here */
+ [X86_TRAP_BP] = exc_int3,
+ [X86_TRAP_OF] = exc_overflow,
+ [X86_TRAP_BR] = exc_bounds,
+ [X86_TRAP_UD] = exc_invalid_op,
+ [X86_TRAP_NM] = exc_device_not_available,
+ [X86_TRAP_DF] = fred_exc_double_fault,
+ [X86_TRAP_OLD_MF] = fred_bad_event, /* 387 only! */
+ [X86_TRAP_TS] = fred_exc_invalid_tss,
+ [X86_TRAP_NP] = fred_exc_segment_not_present,
+ [X86_TRAP_SS] = fred_exc_stack_segment,
+ [X86_TRAP_GP] = fred_exc_general_protection,
+ [X86_TRAP_PF] = fred_exc_page_fault,
+ [X86_TRAP_SPURIOUS] = fred_bad_event, /* Interrupts are their own event type */
+ [X86_TRAP_MF] = exc_coprocessor_error,
+ [X86_TRAP_AC] = fred_exc_alignment_check,
+ [X86_TRAP_MC] = fred_exc_machine_check,
+ [X86_TRAP_XF] = exc_simd_coprocessor_error,
+ [X86_TRAP_VE...NUM_EXCEPTION_VECTORS-1] = fred_bad_event
+ };
+ u8 vector = array_index_nospec((u8)regs->vector, NUM_EXCEPTION_VECTORS);
+
+ exception_handlers[vector](regs);
+}
+
+static __always_inline void fred_emulate_trap(struct pt_regs *regs)
+{
+ regs->type = EVENT_TYPE_SWFAULT;
+ regs->orig_ax = 0;
+ fred_exception(regs);
+}
+
+static __always_inline void fred_emulate_fault(struct pt_regs *regs)
+{
+ regs->ip -= regs->instr_len;
+ fred_emulate_trap(regs);
+}
+
+/*
+ * Emulate SYSENTER if applicable. This is not the preferred system
+ * call in 32-bit mode under FRED, rather int $0x80 is preferred and
+ * exported in the vdso. SYSCALL proper has a hard-coded early out in
+ * fred_entry_from_user().
+ */
+static DEFINE_FRED_HANDLER(fred_syscall_slow)
+{
+ if (IS_ENABLED(CONFIG_IA32_EMULATION) &&
+ likely(regs->vector == FRED_SYSENTER)) {
+ /* Convert frame to a syscall frame */
+ regs->orig_ax = regs->ax;
+ regs->ax = -ENOSYS;
+ do_fast_syscall_32(regs);
+ } else {
+ regs->vector = X86_TRAP_UD;
+ fred_emulate_fault(regs);
+ }
+}
+
+/*
+ * Some software exceptions can also be triggered as int instructions,
+ * for historical reasons. Implement those here. The performance-critical
+ * int $0x80 (32-bit system call) has a hard-coded early out.
+ */
+static DEFINE_FRED_HANDLER(fred_sw_interrupt_user)
+{
+ if (IS_ENABLED(CONFIG_IA32_EMULATION) &&
+ likely(regs->vector == IA32_SYSCALL_VECTOR)) {
+ /* Convert frame to a syscall frame */
+ regs->orig_ax = regs->ax;
+ regs->ax = -ENOSYS;
+ return do_int80_syscall_32(regs);
+ }
+
+ switch (regs->vector) {
+ case X86_TRAP_BP:
+ case X86_TRAP_OF:
+ fred_emulate_trap(regs);
+ break;
+ default:
+ regs->vector = X86_TRAP_GP;
+ fred_emulate_fault(regs);
+ break;
+ }
+}
+
+static DEFINE_FRED_HANDLER(fred_hw_interrupt)
+{
+ irqentry_state_t state = irqentry_enter(regs);
+
+ instrumentation_begin();
+ external_interrupt(regs, regs->vector);
+ instrumentation_end();
+ irqentry_exit(regs, state);
+}
+
+__visible noinstr void fred_entry_from_user(struct pt_regs *regs)
+{
+ static const fred_handler user_handlers[FRED_EVENT_TYPE_COUNT] =
+ {
+ [EVENT_TYPE_HWINT] = fred_hw_interrupt,
+ [EVENT_TYPE_RESERVED] = fred_bad_event,
+ [EVENT_TYPE_NMI] = fred_exc_nmi,
+ [EVENT_TYPE_SWINT] = fred_sw_interrupt_user,
+ [EVENT_TYPE_HWFAULT] = fred_exception,
+ [EVENT_TYPE_SWFAULT] = fred_exception,
+ [EVENT_TYPE_PRIVSW] = fred_exception,
+ [EVENT_TYPE_OTHER] = fred_syscall_slow
+ };
+
+ /*
+ * FRED employs a two-level event dispatch mechanism, with
+ * the first-level on the type of an event and the second-level
+ * on its vector. Thus a dispatch typically induces 2 calls.
+ * We optimize it by using early outs for the most frequent
+ * events, and syscalls are the first. We may also need early
+ * outs for page faults.
+ */
+ if (likely(regs->type == EVENT_TYPE_OTHER &&
+ regs->vector == FRED_SYSCALL)) {
+ /* Convert frame to a syscall frame */
+ regs->orig_ax = regs->ax;
+ regs->ax = -ENOSYS;
+ do_syscall_64(regs, regs->orig_ax);
+ } else {
+ /* Not a system call */
+ u8 type = array_index_nospec((u8)regs->type, FRED_EVENT_TYPE_COUNT);
+
+ user_handlers[type](regs);
+ }
+}
+
+static DEFINE_FRED_HANDLER(fred_sw_interrupt_kernel)
+{
+ switch (regs->vector) {
+ case X86_TRAP_NMI:
+ fred_exc_nmi(regs);
+ break;
+ default:
+ fred_bad_event(regs);
+ break;
+ }
+}
+
+__visible noinstr void fred_entry_from_kernel(struct pt_regs *regs)
+{
+ static const fred_handler kernel_handlers[FRED_EVENT_TYPE_COUNT] =
+ {
+ [EVENT_TYPE_HWINT] = fred_hw_interrupt,
+ [EVENT_TYPE_RESERVED] = fred_bad_event,
+ [EVENT_TYPE_NMI] = fred_exc_nmi,
+ [EVENT_TYPE_SWINT] = fred_sw_interrupt_kernel,
+ [EVENT_TYPE_HWFAULT] = fred_exception,
+ [EVENT_TYPE_SWFAULT] = fred_exception,
+ [EVENT_TYPE_PRIVSW] = fred_exception,
+ [EVENT_TYPE_OTHER] = fred_bad_event
+ };
+ u8 type = array_index_nospec((u8)regs->type, FRED_EVENT_TYPE_COUNT);
+
+ /* The pt_regs frame on entry here is an exception frame */
+ kernel_handlers[type](regs);
+}
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 381bc2b8c1c2..7f70ca6f0020 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -82,6 +82,7 @@ static __always_inline void __##func(struct pt_regs *regs)
#define DECLARE_IDTENTRY_ERRORCODE(vector, func) \
asmlinkage void asm_##func(void); \
asmlinkage void xen_asm_##func(void); \
+ __visible void fred_##func(struct pt_regs *regs); \
__visible void func(struct pt_regs *regs, unsigned long error_code)

/**
@@ -106,6 +107,11 @@ __visible noinstr void func(struct pt_regs *regs, \
irqentry_exit(regs, state); \
} \
\
+__visible noinstr void fred_##func(struct pt_regs *regs) \
+{ \
+ func (regs, regs->orig_ax); \
+} \
+ \
static __always_inline void __##func(struct pt_regs *regs, \
unsigned long error_code)

@@ -622,6 +628,8 @@ DECLARE_IDTENTRY_RAW(X86_TRAP_MC, exc_machine_check);
#ifdef CONFIG_XEN_PV
DECLARE_IDTENTRY_RAW(X86_TRAP_MC, xenpv_exc_machine_check);
#endif
+#else
+#define fred_exc_machine_check fred_bad_event
#endif

/* NMI */
--
2.34.1