x86/asm/entry/64/compat: Change the 32-bit sysenter code to use sp0

The ia32 sysenter code loaded the top of the kernel stack into
rsp by loading kernel_stack and then adjusting it.  It can be
simplified to just read sp0 directly.

This requires the addition of a new asm-offsets entry for sp0.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/88ff9006163d296a0665338585c36d9bfb85235d.1425611534.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index ed97463..719db63 100644 (file)
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -113,8 +113,7 @@ ENTRY(ia32_sysenter_target)
        CFI_DEF_CFA     rsp,0
        CFI_REGISTER    rsp,rbp
        SWAPGS_UNSAFE_STACK
-       movq    PER_CPU_VAR(kernel_stack), %rsp
-       addq    $(KERNEL_STACK_OFFSET),%rsp
+       movq    PER_CPU_VAR(init_tss + TSS_sp0), %rsp
        /*
         * No need to follow this irqs on/off section: the syscall
         * disabled irqs, here we enable it straight after entry:

diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index fdcbb4d..5ce6f2d 100644 (file)
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -81,6 +81,7 @@ int main(void)
 #undef ENTRY
 
        OFFSET(TSS_ist, tss_struct, x86_tss.ist);
+       OFFSET(TSS_sp0, tss_struct, x86_tss.sp0);
        BLANK();
 
        DEFINE(__NR_syscall_max, sizeof(syscalls_64) - 1);