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Message-ID: <20240129180502.4069817-25-ardb+git@google.com> Date: Mon, 29 Jan 2024 19:05:07 +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 04/19] x86/startup_64: Simplify calculation of initial page table address From: Ard Biesheuvel <ardb@...nel.org> Determining the address of the initial page table to program into CR3 involves: - taking the physical address - adding the SME encryption mask On the primary entry path, the code is mapped using a 1:1 virtual to physical translation, so the physical address can be taken directly using a RIP-relative LEA instruction. On the secondary entry path, the address can be obtained by taking the offset from the virtual kernel base (__START_kernel_map) and adding the physical kernel base. This is all very straight-forward, but the current code makes a mess of this. Clean this up. Signed-off-by: Ard Biesheuvel <ardb@...nel.org> --- arch/x86/kernel/head_64.S | 25 ++++++-------------- 1 file changed, 7 insertions(+), 18 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 4017a49d7b76..6d24c2014759 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -113,13 +113,11 @@ SYM_CODE_START_NOALIGN(startup_64) call __startup_64 /* Form the CR3 value being sure to include the CR3 modifier */ - addq $(early_top_pgt - __START_KERNEL_map), %rax + leaq early_top_pgt(%rip), %rcx + addq %rcx, %rax #ifdef CONFIG_AMD_MEM_ENCRYPT mov %rax, %rdi - mov %rax, %r14 - - addq phys_base(%rip), %rdi /* * For SEV guests: Verify that the C-bit is correct. A malicious @@ -128,12 +126,6 @@ SYM_CODE_START_NOALIGN(startup_64) * the next RET instruction. */ call sev_verify_cbit - - /* - * Restore CR3 value without the phys_base which will be added - * below, before writing %cr3. - */ - mov %r14, %rax #endif jmp 1f @@ -173,18 +165,18 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) /* Clear %R15 which holds the boot_params pointer on the boot CPU */ xorq %r15, %r15 + /* Derive the runtime physical address of init_top_pgt[] */ + movq phys_base(%rip), %rax + addq $(init_top_pgt - __START_KERNEL_map), %rax + /* * Retrieve the modifier (SME encryption mask if SME is active) to be * added to the initial pgdir entry that will be programmed into CR3. */ #ifdef CONFIG_AMD_MEM_ENCRYPT - movq sme_me_mask, %rax -#else - xorq %rax, %rax + addq sme_me_mask(%rip), %rax #endif - /* Form the CR3 value being sure to include the CR3 modifier */ - addq $(init_top_pgt - __START_KERNEL_map), %rax 1: #ifdef CONFIG_X86_MCE @@ -211,9 +203,6 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) #endif movq %rcx, %cr4 - /* Setup early boot stage 4-/5-level pagetables. */ - addq phys_base(%rip), %rax - /* * Switch to new page-table * -- 2.43.0.429.g432eaa2c6b-goog
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