[PATCH 7/7] x86/kexec: Zero general purpose registers

[Kevin Lampis <kevin.lampis@xxxxxxxxxx>]

Purgatory zeros these general purpose registers before jumping to the
new kernel. When doing kexec on an EFI kernel there is no purgatory so
we need to zero the registers here instead. This change shouldn't affect
the functionality of legacy kexec.

Signed-off-by: Kevin Lampis <klampis@xxxxxxxxxx>

---
 xen/arch/x86/x86_64/kexec_reloc.S | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/xen/arch/x86/x86_64/kexec_reloc.S 
b/xen/arch/x86/x86_64/kexec_reloc.S
index 6a2c839b83..be9e487f7a 100644
--- a/xen/arch/x86/x86_64/kexec_reloc.S
+++ b/xen/arch/x86/x86_64/kexec_reloc.S
@@ -78,6 +78,20 @@ FUNC(kexec_reloc, PAGE_SIZE)
         testq   $KEXEC_RELOC_FLAG_COMPAT, %r8
         jnz     .L_call_32_bit
 
+        xor %edi, %edi
+        xor %eax, %eax
+        xor %ebx, %ebx
+        xor %ecx, %ecx
+        xor %edx, %edx
+        xor %r8d,  %r8d
+        xor %r9d,  %r9d
+        xor %r10d, %r10d
+        xor %r11d, %r11d
+        xor %r12d, %r12d
+        xor %r13d, %r13d
+        xor %r14d, %r14d
+        xor %r15d, %r15d
+
         /* Jump to the image entry point */
         jmp     *%rbp
 
@@ -94,6 +108,13 @@ FUNC(kexec_reloc, PAGE_SIZE)
         lea     compatibility_mode(%rip), %rax
         push    $0x10
         push    %rax
+
+        xor %edi, %edi
+        xor %eax, %eax
+        xor %ebx, %ebx
+        xor %ecx, %ecx
+        xor %edx, %edx
+
         lretq
 END(kexec_reloc)
 
-- 
2.52.0