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x86/entry/64/compat: Fix Xen PV SYSENTER frame setup 

The SYSENTER frame setup was nonsense.  It worked by accident because the
normal code into which the Xen asm jumped (entry_SYSENTER_32/compat) threw
away SP without touching the stack.  entry_SYSENTER_compat was recently
modified such that it relied on having a valid stack pointer, so now the
Xen asm needs to invoke it with a valid stack.

Fix it up like SYSCALL: use the Xen-provided frame and skip the bare
metal prologue.

Fixes: 1c3e5d3f60 ("x86/entry: Make entry_64_compat.S objtool clean")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lkml.kernel.org/r/947880c41ade688ff4836f665d0c9fcaa9bd1201.1593191971.git.luto@kernel.org
This commit is contained in:
Andy Lutomirski 2020-06-26 10:21:13 -07:00 committed by Thomas Gleixner
parent d1721250f3
commit ffae641f57
2 changed files with 17 additions and 4 deletions
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1
arch/x86/entry/entry_64_compat.S
View File

@ -79,6 +79,7 @@ SYM_CODE_START(entry_SYSENTER_compat)
pushfq /* pt_regs->flags (except IF = 0) */
pushq $__USER32_CS /* pt_regs->cs */
pushq $0 /* pt_regs->ip = 0 (placeholder) */
SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */

20
arch/x86/xen/xen-asm_64.S
View File

@ -161,10 +161,22 @@ SYM_FUNC_END(xen_syscall32_target)
/* 32-bit compat sysenter target */
SYM_FUNC_START(xen_sysenter_target)
mov 0*8(%rsp), %rcx
mov 1*8(%rsp), %r11
mov 5*8(%rsp), %rsp
jmp entry_SYSENTER_compat
/*
* NB: Xen is polite and clears TF from EFLAGS for us. This means
* that we don't need to guard against single step exceptions here.
*/
popq %rcx
popq %r11
/*
* Neither Xen nor the kernel really knows what the old SS and
* CS were. The kernel expects __USER32_DS and __USER32_CS, so
* report those values even though Xen will guess its own values.
*/
movq $__USER32_DS, 4*8(%rsp)
movq $__USER32_CS, 1*8(%rsp)
jmp entry_SYSENTER_compat_after_hwframe
SYM_FUNC_END(xen_sysenter_target)
#else /* !CONFIG_IA32_EMULATION */