From 70f748021087b0cec613dbd9d06b127e3b0e60dc Mon Sep 17 00:00:00 2001 From: Julien Grall Date: Mon, 15 Apr 2019 15:37:12 +0100 Subject: [PATCH] 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 Reviewed-by: Andrii Anisov Reviewed-by: Stefano Stabellini --- 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. */ -- 2.30.2