From: Marco Schlumpp <marco@unikraft.io>
Date: Mon, 2 Jan 2023 10:22:18 +0000 (+0100)
Subject: plat/kvm/x86: Stop unwinding at _libkvmplat_entry2
X-Git-Tag: RELEASE-0.13.0~74
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=ce2e3dae5f8d876e38dcdcf0c3a83850cfb98dc8;p=unikraft%2Funikraft.git

plat/kvm/x86: Stop unwinding at _libkvmplat_entry2

The _libkvmplat_entry2 function is called using assembler code that
switches stacks. Therefore, a debugger can't unwind its frame. This
inserts a CFI that marks the previous instruction pointer as undefined.

Signed-off-by: Marco Schlumpp <marco@unikraft.io>
Reviewed-by: Simon Kuenzer <simon@unikraft.io>
Approved-by: Simon Kuenzer <simon@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #700
---

diff --git a/plat/kvm/x86/setup.c b/plat/kvm/x86/setup.c
index c725656e2..e24df5ebc 100644
--- a/plat/kvm/x86/setup.c
+++ b/plat/kvm/x86/setup.c
@@ -11,6 +11,7 @@
 #include <uk/arch/limits.h>
 #include <uk/arch/types.h>
 #include <uk/arch/paging.h>
+#include <uk/asm/cfi.h>
 #include <uk/plat/console.h>
 #include <uk/assert.h>
 #include <uk/essentials.h>
@@ -287,6 +288,13 @@ static inline int cmdline_init(struct ukplat_bootinfo *bi)
 
 static void __noreturn _ukplat_entry2(void)
 {
+	/* It's not possible to unwind past this function, because the stack
+	 * pointer was overwritten in lcpu_arch_jump_to. Therefore, mark the
+	 * previous instruction pointer as undefined, so that debuggers or
+	 * profilers stop unwinding here.
+	 */
+	ukarch_cfi_unwind_end();
+
 	ukplat_entry_argp(NULL, cmdline, cmdline_len);
 
 	ukplat_lcpu_halt();