xen/arm: Skip initializing the BSS section when it is empty

If the BSS section is empty, then the function should return.
If one does not check whether the BSS section is empty or not, then there is a
risk of writing 0s outside of BSS section (which may contain critical data).

Fixes: dac84b66cc9a ("xen: arm64: initial build + config changes, start of day code")
Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index a96d5d35038f66a96e0ae810fc88b451f1062ddc..4ff5c220bccb7858250ea17cd1a200d808663c0b 100644 (file)
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -185,12 +185,15 @@ zero_bss:
         PRINT("- Zero BSS -\r\n")
         mov_w r0, __bss_start        /* r0 := vaddr(__bss_start) */
         mov_w r1, __bss_end          /* r1 := vaddr(__bss_end)   */
+        cmp   r1, r0
+        beq   skip_bss
 
         mov   r2, #0
 1:      str   r2, [r0], #4
         cmp   r0, r1
         blo   1b
 
+skip_bss:
         mov   pc, lr
 ENDPROC(zero_bss)
 

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 14c3720d80f8d910af01f6dfb8c9a3ac1ec00705..72c7b2449829a94bd34c4b47b5807e349e5c2070 100644 (file)
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -346,6 +346,8 @@ FUNC_LOCAL(zero_bss)
         PRINT("- Zero BSS -\r\n")
         ldr   x0, =__bss_start       /* x0 := vaddr(__bss_start) */
         ldr   x1, =__bss_end         /* x1 := vaddr(__bss_end)   */
+        cmp   x1, x0
+        beq   skip_bss
 
 1:      str   xzr, [x0], #8
         cmp   x0, x1