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[XTF PATCH v3 3/3] x86: Poison hypercall page with `int3` rather than `ret`
- To: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
- Date: Mon, 6 Oct 2025 12:25:58 +0200
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- Cc: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 06 Oct 2025 10:28:32 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Making a hypercall with the hypercall page absent should not
have a happy ending. At best it's just weird, but at worst it might
allow an otherwise failing test to pass.
Suggested-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
---
`./xtf-runner -a` passes
v3:
* New patch based on Roger's suggestion
---
arch/x86/hypercall_page.S | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/hypercall_page.S b/arch/x86/hypercall_page.S
index cc6ddc2..de0a991 100644
--- a/arch/x86/hypercall_page.S
+++ b/arch/x86/hypercall_page.S
@@ -6,8 +6,8 @@
.p2align PAGE_SHIFT
GLOBAL(hypercall_page)
- /* Poisoned with `ret` for safety before hypercalls are set up. */
- .fill PAGE_SIZE, 1, 0xc3
+ /* Poisoned with `int3` so a stray hypercall is patently clear */
+ .fill PAGE_SIZE, 1, 0xcc
.type hypercall_page, STT_OBJECT
.size hypercall_page, PAGE_SIZE
--
2.43.0
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