linux-kernel - [RFC PATCH PoC 05/11] HACK: provide __pti_set_user

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Message-ID: <20250423110948.1103030-18-ardb+git@google.com>
Date: Wed, 23 Apr 2025 13:09:54 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, mingo@...nel.org, Ard Biesheuvel <ardb@...nel.org>
Subject: [RFC PATCH PoC 05/11] HACK: provide __pti_set_user_pgtbl() to startup code

From: Ard Biesheuvel <ardb@...nel.org>

The SME startup code may call out to pti_set_user_pgtbl(), which is not
part of the code corpus that is explicitly built to tolerate execution
from the 1:1 mapping of memory.

Hack around this for now by providing an alternative that just returns
the pgd.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/boot/startup/sme.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/boot/startup/sme.c b/arch/x86/boot/startup/sme.c
index 5738b31c8e60..d55b24cd4d08 100644
--- a/arch/x86/boot/startup/sme.c
+++ b/arch/x86/boot/startup/sme.c
@@ -564,3 +564,8 @@ void __head sme_enable(struct boot_params *bp)
 	cc_vendor	= CC_VENDOR_AMD;
 	cc_set_mask(me_mask);
 }
+
+pgd_t __pti_set_user_pgtbl(pgd_t *pgdp, pgd_t pgd)
+{
+	return pgd;
+}
-- 
2.49.0.805.g082f7c87e0-goog