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

[patchbot@xxxxxxx]

commit b75dee16b33a00a90700c703d3d6a93641d5dadf
Author:     Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
AuthorDate: Mon Oct 28 12:45:42 2024 +0000
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Fri Nov 1 13:59:23 2024 +0000

    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@xxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
---
 xen/arch/arm/arm32/head.S | 3 +++
 xen/arch/arm/arm64/head.S | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index a96d5d3503..4ff5c220bc 100644
--- 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 14c3720d80..72c7b24498 100644
--- 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
--
generated by git-patchbot for /home/xen/git/xen.git#staging