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x86/entry/xen: Route #DB correctly on Xen PV
On Xen PV, #DB doesn't use IST. It still needs to be correctly routed
depending on whether it came from user or kernel mode.
Get rid of DECLARE/DEFINE_IDTENTRY_XEN -- it was too hard to follow the
logic. Instead, route #DB and NMI through DECLARE/DEFINE_IDTENTRY_RAW on
Xen, and do the right thing for #DB. Also add more warnings to the
exc_debug* handlers to make this type of failure more obvious.
This fixes various forms of corruption that happen when usermode
triggers #DB on Xen PV.
Fixes: 4c0dcd8350 ("x86/entry: Implement user mode C entry points for #DB and #MCE")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/4163e733cce0b41658e252c6c6b3464f33fdff17.1593795633.git.luto@kernel.org
This commit is contained in:
Andy Lutomirski
Thomas Gleixner
parent
3c73b81a91
commit
f41f082422
@ -398,18 +398,6 @@ __visible noinstr void func(struct pt_regs *regs, \
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#define DEFINE_IDTENTRY_DEBUG DEFINE_IDTENTRY_IST
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#define DEFINE_IDTENTRY_DEBUG_USER DEFINE_IDTENTRY_NOIST
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/**
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* DECLARE_IDTENTRY_XEN - Declare functions for XEN redirect IDT entry points
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* @vector: Vector number (ignored for C)
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* @func: Function name of the entry point
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*
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* Used for xennmi and xendebug redirections. No DEFINE as this is all ASM
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* indirection magic.
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*/
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#define DECLARE_IDTENTRY_XEN(vector, func) \
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asmlinkage void xen_asm_exc_xen##func(void); \
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asmlinkage void asm_exc_xen##func(void)
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#else /* !__ASSEMBLY__ */
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/*
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@ -469,10 +457,6 @@ __visible noinstr void func(struct pt_regs *regs, \
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/* No ASM code emitted for NMI */
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#define DECLARE_IDTENTRY_NMI(vector, func)
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/* XEN NMI and DB wrapper */
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#define DECLARE_IDTENTRY_XEN(vector, func) \
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idtentry vector asm_exc_xen##func exc_##func has_error_code=0
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/*
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* ASM code to emit the common vector entry stubs where each stub is
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* packed into 8 bytes.
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@ -570,11 +554,15 @@ DECLARE_IDTENTRY_MCE(X86_TRAP_MC, exc_machine_check);
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/* NMI */
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DECLARE_IDTENTRY_NMI(X86_TRAP_NMI, exc_nmi);
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DECLARE_IDTENTRY_XEN(X86_TRAP_NMI, nmi);
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#ifdef CONFIG_XEN_PV
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DECLARE_IDTENTRY_RAW(X86_TRAP_NMI, xenpv_exc_nmi);
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#endif
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/* #DB */
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DECLARE_IDTENTRY_DEBUG(X86_TRAP_DB, exc_debug);
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DECLARE_IDTENTRY_XEN(X86_TRAP_DB, debug);
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#ifdef CONFIG_XEN_PV
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DECLARE_IDTENTRY_RAW(X86_TRAP_DB, xenpv_exc_debug);
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#endif
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/* #DF */
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DECLARE_IDTENTRY_DF(X86_TRAP_DF, exc_double_fault);
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@ -865,6 +865,12 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
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instrumentation_begin();
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trace_hardirqs_off_finish();
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/*
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* If something gets miswired and we end up here for a user mode
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* #DB, we will malfunction.
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*/
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WARN_ON_ONCE(user_mode(regs));
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/*
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* Catch SYSENTER with TF set and clear DR_STEP. If this hit a
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* watchpoint at the same time then that will still be handled.
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@ -883,6 +889,12 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
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static __always_inline void exc_debug_user(struct pt_regs *regs,
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unsigned long dr6)
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{
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/*
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* If something gets miswired and we end up here for a kernel mode
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* #DB, we will malfunction.
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*/
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WARN_ON_ONCE(!user_mode(regs));
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idtentry_enter_user(regs);
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instrumentation_begin();
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@ -598,6 +598,26 @@ static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum,
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}
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#ifdef CONFIG_X86_64
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void noist_exc_debug(struct pt_regs *regs);
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DEFINE_IDTENTRY_RAW(xenpv_exc_nmi)
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{
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/* On Xen PV, NMI doesn't use IST. The C part is the sane as native. */
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exc_nmi(regs);
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}
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DEFINE_IDTENTRY_RAW(xenpv_exc_debug)
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{
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/*
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* There's no IST on Xen PV, but we still need to dispatch
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* to the correct handler.
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*/
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if (user_mode(regs))
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noist_exc_debug(regs);
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else
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exc_debug(regs);
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}
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struct trap_array_entry {
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void (*orig)(void);
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void (*xen)(void);
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@ -609,18 +629,18 @@ struct trap_array_entry {
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.xen = xen_asm_##func, \
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.ist_okay = ist_ok }
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#define TRAP_ENTRY_REDIR(func, xenfunc, ist_ok) { \
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#define TRAP_ENTRY_REDIR(func, ist_ok) { \
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.orig = asm_##func, \
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.xen = xen_asm_##xenfunc, \
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.xen = xen_asm_xenpv_##func, \
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.ist_okay = ist_ok }
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static struct trap_array_entry trap_array[] = {
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TRAP_ENTRY_REDIR(exc_debug, exc_xendebug, true ),
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TRAP_ENTRY_REDIR(exc_debug, true ),
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TRAP_ENTRY(exc_double_fault, true ),
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#ifdef CONFIG_X86_MCE
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TRAP_ENTRY(exc_machine_check, true ),
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#endif
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TRAP_ENTRY_REDIR(exc_nmi, exc_xennmi, true ),
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TRAP_ENTRY_REDIR(exc_nmi, true ),
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TRAP_ENTRY(exc_int3, false ),
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TRAP_ENTRY(exc_overflow, false ),
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#ifdef CONFIG_IA32_EMULATION
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@ -29,10 +29,9 @@ _ASM_NOKPROBE(xen_\name)
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.endm
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xen_pv_trap asm_exc_divide_error
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xen_pv_trap asm_exc_debug
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xen_pv_trap asm_exc_xendebug
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xen_pv_trap asm_xenpv_exc_debug
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xen_pv_trap asm_exc_int3
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xen_pv_trap asm_exc_xennmi
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xen_pv_trap asm_xenpv_exc_nmi
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xen_pv_trap asm_exc_overflow
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xen_pv_trap asm_exc_bounds
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xen_pv_trap asm_exc_invalid_op
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