linux-kernel - [PATCH RFC 7/7] x86/sme: Build the code in mem_encrypt

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Date:   Wed, 12 Jul 2023 11:30:11 +0800
From:   "Hou Wenlong" <houwenlong.hwl@...group.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Lai Jiangshan" <jiangshan.ljs@...group.com>,
        "Hou Wenlong" <houwenlong.hwl@...group.com>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE 32-BIT AND 64-BIT" 
        <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH RFC 7/7] x86/sme: Build the code in mem_encrypt_identity.c as PIE

Similar to head64.c, all the code in mem_encrypt_identity.c runs in
identity address. However, it uses inline assembly to use RIP-relative
reference for some globals. Therefore, build the code as PIE to force
the compiler to generate RIP-relative reference, allowing for all inline
assembly to be removed.

Suggested-by: Lai Jiangshan <jiangshan.ljs@...group.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
---
The changes have not been tested on AMD SME.

 arch/x86/mm/Makefile               |  3 +++
 arch/x86/mm/mem_encrypt_identity.c | 31 +++++-------------------------
 2 files changed, 8 insertions(+), 26 deletions(-)

diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index c80febc44cd2..f5d7b22c5f1b 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -32,6 +32,9 @@ obj-y				+= pat/
 # Make sure __phys_addr has no stackprotector
 CFLAGS_physaddr.o		:= -fno-stack-protector
 CFLAGS_mem_encrypt_identity.o	:= -fno-stack-protector
+CFLAGS_mem_encrypt_identity.o 	+= -fPIE -include $(srctree)/include/linux/hidden.h
+
+CFLAGS_REMOVE_mem_encrypt_identity.o += -mcmodel=kernel

 CFLAGS_fault.o := -I $(srctree)/$(src)/../include/asm/trace

diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index 72aeb0f3dec6..2f292ab4e6a9 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -343,13 +343,7 @@ void __head sme_encrypt_kernel(struct boot_params *bp)
 	}
 #endif

-	/*
-	 * We're running identity mapped, so we must obtain the address to the
-	 * SME encryption workarea using rip-relative addressing.
-	 */
-	asm ("lea sme_workarea(%%rip), %0"
-	     : "=r" (workarea_start)
-	     : "p" (sme_workarea));
+	workarea_start = (unsigned long)(void *)sme_workarea;

 	/*
 	 * Calculate required number of workarea bytes needed:
@@ -505,7 +499,7 @@ void __head sme_encrypt_kernel(struct boot_params *bp)

 void __head sme_enable(struct boot_params *bp)
 {
-	const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
+	const char *cmdline_ptr;
 	unsigned int eax, ebx, ecx, edx;
 	unsigned long feature_mask;
 	bool active_by_default;
@@ -578,21 +572,6 @@ void __head sme_enable(struct boot_params *bp)
 		goto out;
 	}

-	/*
-	 * Fixups have not been applied to phys_base yet and we're running
-	 * identity mapped, so we must obtain the address to the SME command
-	 * line argument data using rip-relative addressing.
-	 */
-	asm ("lea sme_cmdline_arg(%%rip), %0"
-	     : "=r" (cmdline_arg)
-	     : "p" (sme_cmdline_arg));
-	asm ("lea sme_cmdline_on(%%rip), %0"
-	     : "=r" (cmdline_on)
-	     : "p" (sme_cmdline_on));
-	asm ("lea sme_cmdline_off(%%rip), %0"
-	     : "=r" (cmdline_off)
-	     : "p" (sme_cmdline_off));
-
 	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT))
 		active_by_default = true;
 	else
@@ -601,12 +580,12 @@ void __head sme_enable(struct boot_params *bp)
 	cmdline_ptr = (const char *)((u64)bp->hdr.cmd_line_ptr |
 				     ((u64)bp->ext_cmd_line_ptr << 32));

-	if (cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer)) < 0)
+	if (cmdline_find_option(cmdline_ptr, sme_cmdline_arg, buffer, sizeof(buffer)) < 0)
 		return;

-	if (!strncmp(buffer, cmdline_on, sizeof(buffer)))
+	if (!strncmp(buffer, sme_cmdline_on, sizeof(buffer)))
 		sme_me_mask = me_mask;
-	else if (!strncmp(buffer, cmdline_off, sizeof(buffer)))
+	else if (!strncmp(buffer, sme_cmdline_off, sizeof(buffer)))
 		sme_me_mask = 0;
 	else
 		sme_me_mask = active_by_default ? me_mask : 0;
--
2.31.1