linux-kernel - [PATCH v3 18/19] x86/sev: Drop inline asm LEA instructions for RIP-relative references

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Date: Mon, 29 Jan 2024 19:05:21 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>, Kevin Loughlin <kevinloughlin@...gle.com>, 
	Tom Lendacky <thomas.lendacky@....com>, Dionna Glaze <dionnaglaze@...gle.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>, linux-arch@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: [PATCH v3 18/19] x86/sev: Drop inline asm LEA instructions for
 RIP-relative references

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

The SEV code that may run early is now built with -fPIC and so there is
no longer a need for explicit RIP-relative references in inline asm,
given that is what the compiler will emit as well.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/kernel/sev-shared.c       | 14 +-------------
 arch/x86/mm/mem_encrypt_identity.c | 11 +----------
 2 files changed, 2 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 481dbd009ce9..1cfbc6d0df89 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -325,21 +325,9 @@ static int __pitext sev_cpuid_hv(struct ghcb *ghcb, struct es_em_ctxt *ctxt,
 		    : __sev_cpuid_hv_msr(leaf);
 }
 
-/*
- * This may be called early while still running on the initial identity
- * mapping. Use RIP-relative addressing to obtain the correct address
- * while running with the initial identity mapping as well as the
- * switch-over to kernel virtual addresses later.
- */
 static const struct snp_cpuid_table *snp_cpuid_get_table(void)
 {
-	void *ptr;
-
-	asm ("lea cpuid_table_copy(%%rip), %0"
-	     : "=r" (ptr)
-	     : "p" (&cpuid_table_copy));
-
-	return ptr;
+	return &cpuid_table_copy;
 }
 
 /*
diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index bc39e04de980..d01e6b1256c6 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -85,7 +85,6 @@ struct sme_populate_pgd_data {
  */
 static char sme_workarea[2 * PMD_SIZE] __section(".init.scratch");
 
-
 static void __pitext sme_clear_pgd(struct sme_populate_pgd_data *ppd)
 {
 	unsigned long pgd_start, pgd_end, pgd_size;
@@ -329,14 +328,6 @@ void __pitext 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));
-
 	/*
 	 * Calculate required number of workarea bytes needed:
 	 *   executable encryption area size:
@@ -346,7 +337,7 @@ void __pitext sme_encrypt_kernel(struct boot_params *bp)
 	 *   pagetable structures for the encryption of the kernel
 	 *   pagetable structures for workarea (in case not currently mapped)
 	 */
-	execute_start = workarea_start;
+	execute_start = workarea_start = (unsigned long)sme_workarea;
 	execute_end = execute_start + (PAGE_SIZE * 2) + PMD_SIZE;
 	execute_len = execute_end - execute_start;
 
-- 
2.43.0.429.g432eaa2c6b-goog