[Xen-changelog] [xen master] x86/boot: Map the trampoline as read-only

[patchbot@xxxxxxx]

commit 30e6fb5b90a1bb56c7985b8d1600fb9d8da9d34d
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Jan 6 13:36:30 2020 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed Jan 8 18:47:54 2020 +0000

    x86/boot: Map the trampoline as read-only
    
    c/s ec92fcd1d08, which caused the trampoline GDT Access bits to be set,
    removed the final writes which occurred between enabling paging and 
switching
    to the high mappings.  There don't plausibly need to be any memory writes in
    few instructions is takes to perform this transition.
    
    As a consequence, we can remove the RWX mapping of the trampoline.  It is RX
    via its identity mapping below 1M, and RW via the directmap.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/x86_64/mm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/x86_64/mm.c b/xen/arch/x86/x86_64/mm.c
index 8ea09ecc30..b7ce833ffc 100644
--- a/xen/arch/x86/x86_64/mm.c
+++ b/xen/arch/x86/x86_64/mm.c
@@ -699,7 +699,7 @@ void __init zap_low_mappings(void)
     /* Replace with mapping of the boot trampoline only. */
     map_pages_to_xen(trampoline_phys, maddr_to_mfn(trampoline_phys),
                      PFN_UP(trampoline_end - trampoline_start),
-                     __PAGE_HYPERVISOR);
+                     __PAGE_HYPERVISOR_RX);
 }
 
 int setup_compat_arg_xlat(struct vcpu *v)
--
generated by git-patchbot for /home/xen/git/xen.git#master

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