linux-kernel - [RFC PATCH v2.1 03/30] x86/sgx: Add wrapper for SGX2 EMODT function

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Message-Id: <20220304093524.397485-3-jarkko@kernel.org>
Date:   Fri,  4 Mar 2022 11:34:57 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     linux-sgx@...r.kernel.org
Cc:     Nathaniel McCallum <nathaniel@...fian.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND
        64-BIT))
Subject: [RFC PATCH v2.1 03/30] x86/sgx: Add wrapper for SGX2 EMODT function

From: Reinette Chatre <reinette.chatre@...el.com>

Add a wrapper for the EMODT ENCLS leaf function used to
change the type of an enclave page as maintained in the
SGX hardware's Enclave Page Cache Map (EPCM).

EMODT:
1) Updates the EPCM page type of the enclave page.
2) Sets the MODIFIED bit in the EPCM entry of the enclave page.
   This bit is reset by the enclave by invoking ENCLU leaf
   function EACCEPT or EACCEPTCOPY.

Access from within the enclave to the enclave page is not possible
while the MODIFIED bit is set.

After changing the enclave page type by issuing EMODT the kernel
needs to collaborate with the hardware to ensure that no logical
processor continues to hold a reference to the changed page. This
is required to ensure no required security checks are circumvented
and is required for the enclave's EACCEPT/EACCEPTCOPY to succeed.
Ensuring that no references to the changed page remain is
accomplished with the ETRACK flow.

Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
---
 arch/x86/kernel/cpu/sgx/encls.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
index 2b091912f038..7a1ecf704ec1 100644
--- a/arch/x86/kernel/cpu/sgx/encls.h
+++ b/arch/x86/kernel/cpu/sgx/encls.h
@@ -221,4 +221,10 @@ static inline int __emodpr(struct sgx_secinfo *secinfo, void *addr)
 	return __encls_ret_2(EMODPR, secinfo, addr);
 }

+/* Change the type of an EPC page. */
+static inline int __emodt(struct sgx_secinfo *secinfo, void *addr)
+{
+	return __encls_ret_2(EMODT, secinfo, addr);
+}
+
 #endif /* _X86_ENCLS_H */
-- 
2.35.1