[Xen-changelog] [xen stable-4.12] xen/arm: Ensure the SSBD workaround is re-enabled right after exiting a guest

[patchbot@xxxxxxx]

commit 26d307a322ed9ccc62aa18db632f9dd4611934ce
Author:     Julien Grall <julien.grall@xxxxxxx>
AuthorDate: Mon Sep 23 17:45:22 2019 +0100
Commit:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
CommitDate: Wed Nov 27 14:30:49 2019 -0800

    xen/arm: Ensure the SSBD workaround is re-enabled right after exiting a 
guest
    
    At the moment, SSBD workaround is re-enabled for Xen after interrupts
    are unmasked. This means we may end up to execute some part of the
    hypervisor if an interrupt is received before the workaround is
    re-enabled.
    
    Each trap may require to unmask different interrupts.
    As the rest of enter_hypervisor_from_guest() does not require to have
    interrupts masked, the function is now split in two parts:
        1) enter_hypervisor_from_guest_preirq() called with interrupts
           masked.
        2) enter_hypervisor_from_guest() called with interrupts unmasked.
    
    Note that while it might be possible to avoid spliting the function in
    two parts, it requires a bit more work than I can currently invest to
    avoid using indirect branch.
    
    Furthermore, the function name is rather generic as there might be more
    work to dob before interrupts are unmasked in the future.
    
    Fixes: a7898e4c59 ("xen/arm: Add ARCH_WORKAROUND_2 support for guests")
    Reported-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
    Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
    Release-acked-by: Juergen Gross <jgross@xxxxxxxx>
    (cherry picked from commit efee8ba9bf84d54e752f2a44c510cdfb3cc0c282)
---
 xen/arch/arm/arm32/entry.S |  2 +-
 xen/arch/arm/arm64/entry.S |  1 +
 xen/arch/arm/traps.c       | 14 ++++++++++++--
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
index 59a296a4ad..d5c2982e4a 100644
--- a/xen/arch/arm/arm32/entry.S
+++ b/xen/arch/arm/arm32/entry.S
@@ -118,7 +118,7 @@ abort_guest_exit_end:
         bne return_from_trap
 
 skip_check:
-        mov pc, lr
+        b   enter_hypervisor_from_guest_preirq
 ENDPROC(prepare_context_from_guest)
 
         /*
diff --git a/xen/arch/arm/arm64/entry.S b/xen/arch/arm/arm64/entry.S
index 8c9963c50b..c476108b7b 100644
--- a/xen/arch/arm/arm64/entry.S
+++ b/xen/arch/arm/arm64/entry.S
@@ -196,6 +196,7 @@ lr      .req    x30             /* link register */
         ALTERNATIVE("bl check_pending_vserror; cbnz x0, 1f",
                     "nop; nop",
                     SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT)
+        bl      enter_hypervisor_from_guest_preirq
         msr     daifclr, \iflags
         bl      enter_hypervisor_from_guest
         mov     x0, sp
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 53cbaca400..ae7bab6c0e 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1978,15 +1978,25 @@ static inline bool needs_ssbd_flip(struct vcpu *v)
 
 /*
  * Actions that needs to be done after entering the hypervisor from the
- * guest and before we handle any request.
+ * guest and before the interrupts are unmasked.
  */
-void enter_hypervisor_from_guest(void)
+void enter_hypervisor_from_guest_preirq(void)
 {
     struct vcpu *v = current;
 
     /* If the guest has disabled the workaround, bring it back on. */
     if ( needs_ssbd_flip(v) )
         arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_2_FID, 1, NULL);
+}
+
+/*
+ * Actions that needs to be done after entering the hypervisor from the
+ * guest and before we handle any request. Depending on the exception trap,
+ * this may be called with interrupts unmasked.
+ */
+void enter_hypervisor_from_guest(void)
+{
+    struct vcpu *v = current;
 
     /*
      * If we pended a virtual abort, preserve it until it gets cleared.
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12

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