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x86_64, traps: Stop using IST for #SS
On a 32-bit kernel, this has no effect, since there are no IST stacks. On a 64-bit kernel, #SS can only happen in user code, on a failed iret to user space, a canonical violation on access via RSP or RBP, or a genuine stack segment violation in 32-bit kernel code. The first two cases don't need IST, and the latter two cases are unlikely fatal bugs, and promoting them to double faults would be fine. This fixes a bug in which the espfix64 code mishandles a stack segment violation. This saves 4k of memory per CPU and a tiny bit of code. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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6 changed files with 8 additions and 26 deletions
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@ -20,7 +20,6 @@
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#define THREAD_SIZE_ORDER 1
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#define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER)
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#define STACKFAULT_STACK 0
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#define DOUBLEFAULT_STACK 1
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#define NMI_STACK 0
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#define DEBUG_STACK 0
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@ -14,12 +14,11 @@
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#define IRQ_STACK_ORDER 2
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#define IRQ_STACK_SIZE (PAGE_SIZE << IRQ_STACK_ORDER)
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#define STACKFAULT_STACK 1
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#define DOUBLEFAULT_STACK 2
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#define NMI_STACK 3
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#define DEBUG_STACK 4
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#define MCE_STACK 5
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#define N_EXCEPTION_STACKS 5 /* hw limit: 7 */
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#define DOUBLEFAULT_STACK 1
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#define NMI_STACK 2
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#define DEBUG_STACK 3
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#define MCE_STACK 4
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#define N_EXCEPTION_STACKS 4 /* hw limit: 7 */
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#define PUD_PAGE_SIZE (_AC(1, UL) << PUD_SHIFT)
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#define PUD_PAGE_MASK (~(PUD_PAGE_SIZE-1))
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@ -39,6 +39,7 @@ asmlinkage void simd_coprocessor_error(void);
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#ifdef CONFIG_TRACING
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asmlinkage void trace_page_fault(void);
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#define trace_stack_segment stack_segment
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#define trace_divide_error divide_error
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#define trace_bounds bounds
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#define trace_invalid_op invalid_op
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@ -24,7 +24,6 @@ static char x86_stack_ids[][8] = {
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[ DEBUG_STACK-1 ] = "#DB",
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[ NMI_STACK-1 ] = "NMI",
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[ DOUBLEFAULT_STACK-1 ] = "#DF",
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[ STACKFAULT_STACK-1 ] = "#SS",
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[ MCE_STACK-1 ] = "#MC",
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#if DEBUG_STKSZ > EXCEPTION_STKSZ
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[ N_EXCEPTION_STACKS ...
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@ -1259,7 +1259,7 @@ apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \
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idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK
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idtentry int3 do_int3 has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK
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idtentry stack_segment do_stack_segment has_error_code=1 paranoid=1
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idtentry stack_segment do_stack_segment has_error_code=1
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#ifdef CONFIG_XEN
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idtentry xen_debug do_debug has_error_code=0
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idtentry xen_int3 do_int3 has_error_code=0
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@ -233,27 +233,11 @@ DO_ERROR(X86_TRAP_UD, SIGILL, "invalid opcode", invalid_op)
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DO_ERROR(X86_TRAP_OLD_MF, SIGFPE, "coprocessor segment overrun",coprocessor_segment_overrun)
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DO_ERROR(X86_TRAP_TS, SIGSEGV, "invalid TSS", invalid_TSS)
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DO_ERROR(X86_TRAP_NP, SIGBUS, "segment not present", segment_not_present)
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#ifdef CONFIG_X86_32
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DO_ERROR(X86_TRAP_SS, SIGBUS, "stack segment", stack_segment)
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#endif
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DO_ERROR(X86_TRAP_AC, SIGBUS, "alignment check", alignment_check)
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#ifdef CONFIG_X86_64
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/* Runs on IST stack */
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dotraplinkage void do_stack_segment(struct pt_regs *regs, long error_code)
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{
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enum ctx_state prev_state;
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prev_state = exception_enter();
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if (notify_die(DIE_TRAP, "stack segment", regs, error_code,
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X86_TRAP_SS, SIGBUS) != NOTIFY_STOP) {
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preempt_conditional_sti(regs);
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do_trap(X86_TRAP_SS, SIGBUS, "stack segment", regs, error_code, NULL);
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preempt_conditional_cli(regs);
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}
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exception_exit(prev_state);
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}
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dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
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{
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static const char str[] = "double fault";
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@ -802,7 +786,7 @@ void __init trap_init(void)
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set_intr_gate(X86_TRAP_OLD_MF, coprocessor_segment_overrun);
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set_intr_gate(X86_TRAP_TS, invalid_TSS);
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set_intr_gate(X86_TRAP_NP, segment_not_present);
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set_intr_gate_ist(X86_TRAP_SS, &stack_segment, STACKFAULT_STACK);
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set_intr_gate(X86_TRAP_SS, stack_segment);
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set_intr_gate(X86_TRAP_GP, general_protection);
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set_intr_gate(X86_TRAP_SPURIOUS, spurious_interrupt_bug);
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set_intr_gate(X86_TRAP_MF, coprocessor_error);
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