[Xen-changelog] [xen staging] xen/arm32: head: Always zero r3 before update a page-table entry

[patchbot@xxxxxxx]

commit 70f748021087b0cec613dbd9d06b127e3b0e60dc
Author:     Julien Grall <julien.grall@xxxxxxx>
AuthorDate: Mon Apr 15 15:37:12 2019 +0100
Commit:     Julien Grall <julien.grall@xxxxxxx>
CommitDate: Thu Jun 6 18:44:33 2019 +0100

    xen/arm32: head: Always zero r3 before update a page-table entry
    
    The boot code is using r2 and r3 to hold the page-table entry value.
    While r2 is always updated before storing the value, this is not always
    the case for r3.
    
    Thankfully today, r3 will always be zero when we care. But this is
    difficult to track and error-prone.
    
    So always zero r3 within the few instructions before the write the
    page-table entry.
    
    Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
    Reviewed-by: Andrii Anisov <andrii.anisov@xxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/arm32/head.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 598806b706..396cbc89c3 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -280,6 +280,7 @@ cpu_init_done:
         orr   r2, r2, #PT_UPPER(MEM) /* r2:r3 := section map */
         orr   r2, r2, #PT_LOWER(MEM)
         lsl   r1, r1, #3             /* r1 := Slot offset */
+        mov   r3, #0x0
         strd  r2, r3, [r4, r1]       /* Mapping of paddr(start) */
         mov   r6, #1                 /* r6 := identity map now in place */
 
@@ -382,11 +383,11 @@ paging:
 
         /* Add UART to the fixmap table */
         ldr   r1, =xen_fixmap        /* r1 := vaddr (xen_fixmap) */
-        mov   r3, #0
         lsr   r2, r11, #THIRD_SHIFT
         lsl   r2, r2, #THIRD_SHIFT   /* 4K aligned paddr of UART */
         orr   r2, r2, #PT_UPPER(DEV_L3)
         orr   r2, r2, #PT_LOWER(DEV_L3) /* r2:r3 := 4K dev map including UART 
*/
+        mov   r3, #0x0
         strd  r2, r3, [r1, #(FIXMAP_CONSOLE*8)] /* Map it in the first 
fixmap's slot */
 1:
 
@@ -398,6 +399,7 @@ paging:
         orr   r2, r2, #PT_LOWER(PT)  /* r2:r3 := table map of xen_fixmap */
         ldr   r4, =FIXMAP_ADDR(0)
         mov   r4, r4, lsr #(SECOND_SHIFT - 3)   /* r4 := Slot for FIXMAP(0) */
+        mov   r3, #0x0
         strd  r2, r3, [r1, r4]       /* Map it in the fixmap's slot */
 
         /* Use a virtual address to access the UART. */
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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