x86_64, traps: Stop using IST for #SS

commit 6f442be2fb22be02cafa606f1769fa1e6f894441 upstream.

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h
index ef17af0134750203f803f5a665a86178abfa2107..4376b458aef76b8a1f94bfc882526049618a7be1 100644 (file)
--- a/arch/x86/include/asm/page_32_types.h
+++ b/arch/x86/include/asm/page_32_types.h
@@ -18,7 +18,6 @@
 #define THREAD_SIZE_ORDER      1
 #define THREAD_SIZE            (PAGE_SIZE << THREAD_SIZE_ORDER)
 
-#define STACKFAULT_STACK 0
 #define DOUBLEFAULT_STACK 1
 #define NMI_STACK 0
 #define DEBUG_STACK 0

diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
index 6c896fbe21db50fca525bb321aceab47172ee9d4..970f3097ee33b9801ee5526656c0c9e3e1cb680e 100644 (file)
--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -14,12 +14,11 @@
 #define IRQ_STACK_ORDER 2
 #define IRQ_STACK_SIZE (PAGE_SIZE << IRQ_STACK_ORDER)
 
-#define STACKFAULT_STACK 1
-#define DOUBLEFAULT_STACK 2
-#define NMI_STACK 3
-#define DEBUG_STACK 4
-#define MCE_STACK 5
-#define N_EXCEPTION_STACKS 5  /* hw limit: 7 */
+#define DOUBLEFAULT_STACK 1
+#define NMI_STACK 2
+#define DEBUG_STACK 3
+#define MCE_STACK 4
+#define N_EXCEPTION_STACKS 4  /* hw limit: 7 */
 
 #define PUD_PAGE_SIZE          (_AC(1, UL) << PUD_SHIFT)
 #define PUD_PAGE_MASK          (~(PUD_PAGE_SIZE-1))

diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index addb207dab92d11ebe4d48650babe07db36a1539..66e274a3d968eb9b382dea4ba13d34169beb8bed 100644 (file)
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -24,7 +24,6 @@ static char x86_stack_ids[][8] = {
                [ DEBUG_STACK-1                 ]       = "#DB",
                [ NMI_STACK-1                   ]       = "NMI",
                [ DOUBLEFAULT_STACK-1           ]       = "#DF",
-               [ STACKFAULT_STACK-1            ]       = "#SS",
                [ MCE_STACK-1                   ]       = "#MC",
 #if DEBUG_STKSZ > EXCEPTION_STKSZ
                [ N_EXCEPTION_STACKS ...

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index b8570b1c72d846a74fc3be16862ffeefb8344d62..6b4472b4db50e1619db393e1040bbac71502ad9a 100644 (file)
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1503,7 +1503,7 @@ apicinterrupt HYPERVISOR_CALLBACK_VECTOR \
 
 paranoidzeroentry_ist debug do_debug DEBUG_STACK
 paranoidzeroentry_ist int3 do_int3 DEBUG_STACK
-paranoiderrorentry stack_segment do_stack_segment
+errorentry stack_segment do_stack_segment
 #ifdef CONFIG_XEN
 zeroentry xen_debug do_debug
 zeroentry xen_int3 do_int3

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 74e080123ec927b5619077616933f52371558ead..00a287358470df63f999ab953ea77c68dd22f2f3 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -220,28 +220,12 @@ DO_ERROR(X86_TRAP_OLD_MF, SIGFPE, "coprocessor segment overrun",
                coprocessor_segment_overrun)
 DO_ERROR(X86_TRAP_TS, SIGSEGV, "invalid TSS", invalid_TSS)
 DO_ERROR(X86_TRAP_NP, SIGBUS, "segment not present", segment_not_present)
-#ifdef CONFIG_X86_32
 DO_ERROR(X86_TRAP_SS, SIGBUS, "stack segment", stack_segment)
-#endif
 DO_ERROR_INFO(X86_TRAP_AC, SIGBUS, "alignment check", alignment_check,
                BUS_ADRALN, 0)
 
 #ifdef CONFIG_X86_64
 /* Runs on IST stack */
-dotraplinkage void do_stack_segment(struct pt_regs *regs, long error_code)
-{
-       enum ctx_state prev_state;
-
-       prev_state = exception_enter();
-       if (notify_die(DIE_TRAP, "stack segment", regs, error_code,
-                      X86_TRAP_SS, SIGBUS) != NOTIFY_STOP) {
-               preempt_conditional_sti(regs);
-               do_trap(X86_TRAP_SS, SIGBUS, "stack segment", regs, error_code, NULL);
-               preempt_conditional_cli(regs);
-       }
-       exception_exit(prev_state);
-}
-
 dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 {
        static const char str[] = "double fault";
@@ -769,7 +753,7 @@ void __init trap_init(void)
        set_intr_gate(X86_TRAP_OLD_MF, &coprocessor_segment_overrun);
        set_intr_gate(X86_TRAP_TS, &invalid_TSS);
        set_intr_gate(X86_TRAP_NP, &segment_not_present);
-       set_intr_gate_ist(X86_TRAP_SS, &stack_segment, STACKFAULT_STACK);
+       set_intr_gate(X86_TRAP_SS, stack_segment);
        set_intr_gate(X86_TRAP_GP, &general_protection);
        set_intr_gate(X86_TRAP_SPURIOUS, &spurious_interrupt_bug);
        set_intr_gate(X86_TRAP_MF, &coprocessor_error);