The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 29b810f5a5ec127d3143770098e05981baa3eb77 Gitweb: https://git.kernel.org/tip/29b810f5a5ec127d3143770098e05981baa3eb77 Author: Jan Beulich jbeulich@suse.com AuthorDate: Mon, 11 Nov 2019 15:32:12 +01:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Tue, 19 Nov 2019 21:58:28 +01:00

x86/xen/32: Make xen_iret_crit_fixup() independent of frame layout

Now that SS:ESP always get saved by SAVE_ALL, this also needs to be accounted for in xen_iret_crit_fixup(). Otherwise the old_ax value gets interpreted as EFLAGS, and hence VM86 mode appears to be active all the time, leading to random "vm86_32: no user_vm86: BAD" log messages alongside processes randomly crashing.

Since following the previous model (sitting after SAVE_ALL) would further complicate the code _and_ retain the dependency of xen_iret_crit_fixup() on frame manipulations done by entry_32.S, switch things around and do the adjustment ahead of SAVE_ALL.

Fixes: 3c88c692c287 ("x86/stackframe/32: Provide consistent pt_regs") Signed-off-by: Jan Beulich jbeulich@suse.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Juergen Gross jgross@suse.com Cc: Stable Team stable@vger.kernel.org Link: https://lkml.kernel.org/r/32d8713d-25a7-84ab-b74b-aa3e88abce6b@suse.com

--- arch/x86/entry/entry_32.S | 22 +++++-------- arch/x86/xen/xen-asm_32.S | 66 +++++++++++++------------------------- 2 files changed, 33 insertions(+), 55 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 3f847d8..019dbac 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -1341,11 +1341,6 @@ END(spurious_interrupt_bug)

#ifdef CONFIG_XEN_PV ENTRY(xen_hypervisor_callback) - pushl $-1 /* orig_ax = -1 => not a system call */ - SAVE_ALL - ENCODE_FRAME_POINTER - TRACE_IRQS_OFF - /* * Check to see if we got the event in the critical * region in xen_iret_direct, after we've reenabled @@ -1353,16 +1348,17 @@ ENTRY(xen_hypervisor_callback) * iret instruction's behaviour where it delivers a * pending interrupt when enabling interrupts: */ - movl PT_EIP(%esp), %eax - cmpl $xen_iret_start_crit, %eax + cmpl $xen_iret_start_crit, (%esp) jb 1f - cmpl $xen_iret_end_crit, %eax + cmpl $xen_iret_end_crit, (%esp) jae 1f - - jmp xen_iret_crit_fixup - -ENTRY(xen_do_upcall) -1: mov %esp, %eax + call xen_iret_crit_fixup +1: + pushl $-1 /* orig_ax = -1 => not a system call */ + SAVE_ALL + ENCODE_FRAME_POINTER + TRACE_IRQS_OFF + mov %esp, %eax call xen_evtchn_do_upcall #ifndef CONFIG_PREEMPTION call xen_maybe_preempt_hcall diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S index c15db06..392e033 100644 --- a/arch/x86/xen/xen-asm_32.S +++ b/arch/x86/xen/xen-asm_32.S @@ -126,10 +126,9 @@ hyper_iret: .globl xen_iret_start_crit, xen_iret_end_crit

/* - * This is called by xen_hypervisor_callback in entry.S when it sees + * This is called by xen_hypervisor_callback in entry_32.S when it sees * that the EIP at the time of interrupt was between - * xen_iret_start_crit and xen_iret_end_crit. We're passed the EIP in - * %eax so we can do a more refined determination of what to do. + * xen_iret_start_crit and xen_iret_end_crit. * * The stack format at this point is: * ---------------- @@ -138,34 +137,23 @@ hyper_iret: * eflags } outer exception info * cs } * eip } - * ---------------- <- edi (copy dest) - * eax : outer eax if it hasn't been restored * ---------------- - * eflags } nested exception info - * cs } (no ss/esp because we're nested - * eip } from the same ring) - * orig_eax }<- esi (copy src) - * - - - - - - - - - * fs } - * es } - * ds } SAVE_ALL state - * eax } - * : : - * ebx }<- esp + * eax : outer eax if it hasn't been restored * ---------------- + * eflags } + * cs } nested exception info + * eip } + * return address : (into xen_hypervisor_callback) * - * In order to deliver the nested exception properly, we need to shift - * everything from the return addr up to the error code so it sits - * just under the outer exception info. This means that when we - * handle the exception, we do it in the context of the outer - * exception rather than starting a new one. + * In order to deliver the nested exception properly, we need to discard the + * nested exception frame such that when we handle the exception, we do it + * in the context of the outer exception rather than starting a new one. * - * The only caveat is that if the outer eax hasn't been restored yet - * (ie, it's still on stack), we need to insert its value into the - * SAVE_ALL state before going on, since it's usermode state which we - * eventually need to restore. + * The only caveat is that if the outer eax hasn't been restored yet (i.e. + * it's still on stack), we need to restore its value here. */ ENTRY(xen_iret_crit_fixup) + pushl %ecx /* * Paranoia: Make sure we're really coming from kernel space. * One could imagine a case where userspace jumps into the @@ -176,32 +164,26 @@ ENTRY(xen_iret_crit_fixup) * jump instruction itself, not the destination, but some * virtual environments get this wrong. */ - movl PT_CS(%esp), %ecx + movl 3*4(%esp), %ecx /* nested CS */ andl $SEGMENT_RPL_MASK, %ecx cmpl $USER_RPL, %ecx + popl %ecx je 2f

- lea PT_ORIG_EAX(%esp), %esi - lea PT_EFLAGS(%esp), %edi - /* * If eip is before iret_restore_end then stack * hasn't been restored yet. */ - cmp $iret_restore_end, %eax + cmpl $iret_restore_end, 1*4(%esp) jae 1f

- movl 0+4(%edi), %eax /* copy EAX (just above top of frame) */ - movl %eax, PT_EAX(%esp) + movl 4*4(%esp), %eax /* load outer EAX */ + ret $4*4 /* discard nested EIP, CS, and EFLAGS as + * well as the just restored EAX */

- lea ESP_OFFSET(%edi), %edi /* move dest up over saved regs */ - - /* set up the copy */ -1: std - mov $PT_EIP / 4, %ecx /* saved regs up to orig_eax */ - rep movsl - cld - - lea 4(%edi), %esp /* point esp to new frame */ -2: jmp xen_do_upcall +1: + ret $3*4 /* discard nested EIP, CS, and EFLAGS */

+2: + ret +END(xen_iret_crit_fixup)