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x86/entry: Make syscall/sysenter entrypoints CET-IBT compatible
Each of MSR_{L,C}STAR and MSR_SYSENTER_EIP need to land on an endbr64
instruction. For sysenter, this is easy.
Unfortunately for syscall, the stubs are already 29 byte long with a limit of
32. endbr64 is 4 bytes. Luckily, there is a 1 byte instruction which can
move from the stubs into the main handlers.
Move the push %rax out of the stub and into {l,c}star_entry(), allowing room
for the endbr64 instruction when appropriate. Update the comment describing
the entry state.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
This commit is contained in:
Andrew Cooper committed
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2 files changed
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@@ -241,18 +241,17 @@ iret_exit_to_guest:
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* When entering SYSCALL from user mode:
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* Vector directly to the registered arch.syscall_addr.
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*
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* Initial work is done by per-CPU trampolines. At this point %rsp has been
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* initialised to point at the correct Xen stack, %rsp has been saved, and
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* %rax needs to be restored from the %ss save slot. All other registers are
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* still to be saved onto the stack, starting with RFLAGS, and an appropriate
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* %ss must be saved into the space left by the trampoline.
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* Initial work is done by per-CPU trampolines.
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* - Guest %rax stored in the %ss slot
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* - Guest %rsp stored in %rax
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* - Xen stack loaded, pointing at the %ss slot
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*/
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ENTRY(lstar_enter)
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#ifdef CONFIG_XEN_SHSTK
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ALTERNATIVE "", "setssbsy", X86_FEATURE_XEN_SHSTK
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#endif
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/* sti could live here when we don't switch page tables below. */
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movq 8(%rsp),%rax /* Restore %rax. */
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push %rax /* Guest %rsp */
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movq 8(%rsp), %rax /* Restore guest %rax */
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movq $FLAT_KERNEL_SS,8(%rsp)
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pushq %r11
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pushq $FLAT_KERNEL_CS64
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@@ -288,9 +287,9 @@ ENTRY(cstar_enter)
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#ifdef CONFIG_XEN_SHSTK
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ALTERNATIVE "", "setssbsy", X86_FEATURE_XEN_SHSTK
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#endif
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/* sti could live here when we don't switch page tables below. */
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push %rax /* Guest %rsp */
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CR4_PV32_RESTORE
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movq 8(%rsp), %rax /* Restore %rax. */
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movq 8(%rsp), %rax /* Restore guest %rax. */
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movq $FLAT_USER_SS32, 8(%rsp) /* Assume a 64bit domain. Compat handled lower. */
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pushq %r11
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pushq $FLAT_USER_CS32
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@@ -323,6 +322,7 @@ ENTRY(cstar_enter)
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jmp switch_to_kernel
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ENTRY(sysenter_entry)
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ENDBR64
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#ifdef CONFIG_XEN_SHSTK
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ALTERNATIVE "", "setssbsy", X86_FEATURE_XEN_SHSTK
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#endif
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@@ -16,6 +16,7 @@
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#include <asm/current.h>
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#include <asm/flushtlb.h>
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#include <asm/traps.h>
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#include <asm/endbr.h>
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#include <asm/event.h>
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#include <asm/nmi.h>
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#include <asm/msr.h>
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@@ -295,6 +296,12 @@ static unsigned int write_stub_trampoline(
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{
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unsigned char *p = stub;
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if ( cpu_has_xen_ibt )
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{
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place_endbr64(p);
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p += 4;
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}
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/* Store guest %rax into %ss slot */
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/* movabsq %rax, stack_bottom - 8 */
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*p++ = 0x48;
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@@ -315,10 +322,6 @@ static unsigned int write_stub_trampoline(
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*(uint64_t *)p = stack_bottom - 8;
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p += 8;
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/* Store guest %rsp into %rsp slot */
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/* pushq %rax */
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*p++ = 0x50;
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/* jmp target_va */
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*p++ = 0xe9;
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*(int32_t *)p = target_va - (stub_va + (p - stub) + 4);
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