[RFC/RFT PATCH 11/19] x86/rethook: Use RIP-relative reference for fake return address

Ard Biesheuvel
2026-01-08T09:28:27Z

Pushing an immediate absolute address to the stack is not permitted when
linking x86_64 code in PIE mode. Usually, the address can be taken using
a RIP-relative LEA instruction, but this is not possible here as there
are no available registers.

So instead, take the address into a static global, and push it onto the
stack using a RIP-relative memory operand.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/kernel/rethook.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/rethook.c b/arch/x86/kernel/rethook.c
index 85e2f2d16a90..50812ac718b0 100644
--- a/arch/x86/kernel/rethook.c
+++ b/arch/x86/kernel/rethook.c
@@ -11,6 +11,10 @@

__visible void arch_rethook_trampoline_callback(struct pt_regs *regs);

+#ifdef CONFIG_X86_64
+static __used void * const __arch_rethook_trampoline = &arch_rethook_trampoline;
+#endif
+
#ifndef ANNOTATE_NOENDBR
#define ANNOTATE_NOENDBR
#endif
@@ -27,7 +31,7 @@ asm(
#ifdef CONFIG_X86_64
ANNOTATE_NOENDBR "\n" /* This is only jumped from ret instruction */
/* Push a fake return address to tell the unwinder it's a rethook. */
- " pushq $arch_rethook_trampoline\n"
+ " pushq __arch_rethook_trampoline(%rip)\n"
UNWIND_HINT_FUNC
" pushq $" __stringify(__KERNEL_DS) "\n"
/* Save the 'sp - 16', this will be fixed later. */
--
2.47.3