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(075-129-116-198.res.spectrum.com. [75.129.116.198]) by smtp.gmail.com with ESMTPSA id b26-20020ac8679a000000b003e6356d28acsm254927qtp.20.2023.03.31.11.28.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 31 Mar 2023 11:28:44 -0700 (PDT) From: Brian Gerst To: linux-kernel@vger.kernel.org, x86@kernel.org Cc: Thomas Gleixner , Borislav Petkov , "H . Peter Anvin" , Peter Zijlstra , Ingo Molnar , Brian Gerst Subject: [PATCH] x86/boot: Clean up handling of boot_params pointer Date: Fri, 31 Mar 2023 14:28:39 -0400 Message-Id: <20230331182839.13960-1-brgerst@gmail.com> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 X-Spam-Status: No, score=-0.2 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1761909684311210317?= X-GMAIL-MSGID: =?utf-8?q?1761909684311210317?= On entry from the bootloader, RSI contains the pointer to the boot_params data structure. Since the RSI register can be clobbered when calling C functions, it is saved and restored around every call. Instead, move it to the R12 register, which is preserved across calls. Signed-off-by: Brian Gerst --- arch/x86/kernel/head_64.S | 29 ++++++++++------------------- 1 file changed, 10 insertions(+), 19 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index a5df3e994f04..0d130ca2e0a3 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -49,8 +49,6 @@ SYM_CODE_START_NOALIGN(startup_64) * for us. These identity mapped page tables map all of the * kernel pages and possibly all of memory. * - * %rsi holds a physical pointer to real_mode_data. - * * We come here either directly from a 64bit bootloader, or from * arch/x86/boot/compressed/head_64.S. * @@ -61,6 +59,12 @@ SYM_CODE_START_NOALIGN(startup_64) * tables and then reload them. */ + /* + * RSI holds a physical pointer to real_mode_data. Move it to R12, + * which is preserved across C function calls. + */ + movq %rsi, %r12 + /* Set up the stack for verify_cpu() */ leaq (__end_init_task - PTREGS_SIZE)(%rip), %rsp @@ -73,9 +77,7 @@ SYM_CODE_START_NOALIGN(startup_64) shrq $32, %rdx wrmsr - pushq %rsi call startup_64_setup_env - popq %rsi #ifdef CONFIG_AMD_MEM_ENCRYPT /* @@ -84,10 +86,8 @@ SYM_CODE_START_NOALIGN(startup_64) * which needs to be done before any CPUID instructions are executed in * subsequent code. */ - movq %rsi, %rdi - pushq %rsi + movq %r12, %rdi call sme_enable - popq %rsi #endif /* Now switch to __KERNEL_CS so IRET works reliably */ @@ -109,9 +109,8 @@ SYM_CODE_START_NOALIGN(startup_64) * programmed into CR3. */ leaq _text(%rip), %rdi - pushq %rsi + movq %r12, %rsi call __startup_64 - popq %rsi /* Form the CR3 value being sure to include the CR3 modifier */ addq $(early_top_pgt - __START_KERNEL_map), %rax @@ -125,8 +124,6 @@ SYM_CODE_START(secondary_startup_64) * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0, * and someone has loaded a mapped page table. * - * %rsi holds a physical pointer to real_mode_data. - * * We come here either from startup_64 (using physical addresses) * or from trampoline.S (using virtual addresses). * @@ -197,13 +194,9 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) * hypervisor could lie about the C-bit position to perform a ROP * attack on the guest by writing to the unencrypted stack and wait for * the next RET instruction. - * %rsi carries pointer to realmode data and is callee-clobbered. Save - * and restore it. */ - pushq %rsi movq %rax, %rdi call sev_verify_cbit - popq %rsi /* * Switch to new page-table @@ -294,9 +287,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) wrmsr /* Setup and Load IDT */ - pushq %rsi call early_setup_idt - popq %rsi /* Check if nx is implemented */ movl $0x80000001, %eax @@ -332,9 +323,9 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) pushq $0 popfq - /* rsi is pointer to real mode structure with interesting info. + /* R12 is pointer to real mode structure with interesting info. pass it to C */ - movq %rsi, %rdi + movq %r12, %rdi .Ljump_to_C_code: /*