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

[Ard Biesheuvel]

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@xxxxxxxxxx>
---
 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