x86/traps: Don't clear segment high bits in early_idt_handler_common()

Now that pt_regs defines the segment fields as 16-bit, there's no
need to sanitize the values.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 1f85ee8f9439fff69f6bc7a38523b38f88311cb0..0332664eb158184419ac5bf96709728174bb97d8 100644 (file)
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -457,12 +457,9 @@ early_idt_handler_common:
        /* The vector number is in pt_regs->gs */
 
        cld
-       pushl   %fs             /* pt_regs->fs */
-       movw    $0, 2(%esp)     /* clear high bits (some CPUs leave garbage) */
-       pushl   %es             /* pt_regs->es */
-       movw    $0, 2(%esp)     /* clear high bits (some CPUs leave garbage) */
-       pushl   %ds             /* pt_regs->ds */
-       movw    $0, 2(%esp)     /* clear high bits (some CPUs leave garbage) */
+       pushl   %fs             /* pt_regs->fs (__fsh varies by model) */
+       pushl   %es             /* pt_regs->es (__esh varies by model) */
+       pushl   %ds             /* pt_regs->ds (__dsh varies by model) */
        pushl   %eax            /* pt_regs->ax */
        pushl   %ebp            /* pt_regs->bp */
        pushl   %edi            /* pt_regs->di */
@@ -479,9 +476,8 @@ early_idt_handler_common:
        /* Load the vector number into EDX */
        movl    PT_GS(%esp), %edx
 
-       /* Load GS into pt_regs->gs and clear high bits */
+       /* Load GS into pt_regs->gs (and maybe clobber __gsh) */
        movw    %gs, PT_GS(%esp)
-       movw    $0, PT_GS+2(%esp)
 
        movl    %esp, %eax      /* args are pt_regs (EAX), trapnr (EDX) */
        call    early_fixup_exception
@@ -493,10 +489,10 @@ early_idt_handler_common:
        popl    %edi            /* pt_regs->di */
        popl    %ebp            /* pt_regs->bp */
        popl    %eax            /* pt_regs->ax */
-       popl    %ds             /* pt_regs->ds */
-       popl    %es             /* pt_regs->es */
-       popl    %fs             /* pt_regs->fs */
-       popl    %gs             /* pt_regs->gs */
+       popl    %ds             /* pt_regs->ds (always ignores __dsh) */
+       popl    %es             /* pt_regs->es (always ignores __esh) */
+       popl    %fs             /* pt_regs->fs (always ignores __fsh) */
+       popl    %gs             /* pt_regs->gs (always ignores __gsh) */
        decl    %ss:early_recursion_flag
        addl    $4, %esp        /* pop pt_regs->orig_ax */
        iret