This is a note to let you know that I've just added the patch titled

x86/efi: Hoist page table switching code into efi_call_virt()

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-efi-hoist-page-table-switching-code-into-efi_call_virt.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From c9f2a9a65e4855b74d92cdad688f6ee4a1a323ff Mon Sep 17 00:00:00 2001

From: Matt Fleming matt@codeblueprint.co.uk Date: Fri, 27 Nov 2015 21:09:33 +0000 Subject: x86/efi: Hoist page table switching code into efi_call_virt()

From: Matt Fleming matt@codeblueprint.co.uk

commit c9f2a9a65e4855b74d92cdad688f6ee4a1a323ff upstream.

This change is a prerequisite for pending patches that switch to a dedicated EFI page table, instead of using 'trampoline_pgd' which shares PGD entries with 'swapper_pg_dir'. The pending patches make it impossible to dereference the runtime service function pointer without first switching %cr3.

It's true that we now have duplicated switching code in efi_call_virt() and efi_call_phys_{prolog,epilog}() but we are sacrificing code duplication for a little more clarity and the ease of writing the page table switching code in C instead of asm.

Signed-off-by: Matt Fleming matt@codeblueprint.co.uk Reviewed-by: Borislav Petkov bp@suse.de Acked-by: Borislav Petkov bp@suse.de Cc: Andrew Morton akpm@linux-foundation.org Cc: Andy Lutomirski luto@amacapital.net Cc: Andy Lutomirski luto@kernel.org Cc: Ard Biesheuvel ard.biesheuvel@linaro.org Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: Dave Jones davej@codemonkey.org.uk Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Sai Praneeth Prakhya sai.praneeth.prakhya@intel.com Cc: Stephen Smalley sds@tycho.nsa.gov Cc: Thomas Gleixner tglx@linutronix.de Cc: Toshi Kani toshi.kani@hp.com Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/1448658575-17029-5-git-send-email-matt@codeblueprin... Signed-off-by: Ingo Molnar mingo@kernel.org Cc: "Ghannam, Yazen" Yazen.Ghannam@amd.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/x86/include/asm/efi.h | 25 ++++++++++++++++++++ arch/x86/platform/efi/efi_64.c | 24 +++++++++----------- arch/x86/platform/efi/efi_stub_64.S | 43 ------------------------------------ 3 files changed, 36 insertions(+), 56 deletions(-)

--- a/arch/x86/include/asm/efi.h +++ b/arch/x86/include/asm/efi.h @@ -3,6 +3,7 @@

#include <asm/fpu/api.h> #include <asm/pgtable.h> +#include <asm/tlb.h>

/* * We map the EFI regions needed for runtime services non-contiguously, @@ -64,6 +65,17 @@ extern u64 asmlinkage efi_call(void *fp,

#define efi_call_phys(f, args...) efi_call((f), args)

+/* + * Scratch space used for switching the pagetable in the EFI stub + */ +struct efi_scratch { + u64 r15; + u64 prev_cr3; + pgd_t *efi_pgt; + bool use_pgd; + u64 phys_stack; +} __packed; + #define efi_call_virt(f, ...) \ ({ \ efi_status_t __s; \ @@ -71,7 +83,20 @@ extern u64 asmlinkage efi_call(void *fp, efi_sync_low_kernel_mappings(); \ preempt_disable(); \ __kernel_fpu_begin(); \ + \ + if (efi_scratch.use_pgd) { \ + efi_scratch.prev_cr3 = read_cr3(); \ + write_cr3((unsigned long)efi_scratch.efi_pgt); \ + __flush_tlb_all(); \ + } \ + \ __s = efi_call((void *)efi.systab->runtime->f, __VA_ARGS__); \ + \ + if (efi_scratch.use_pgd) { \ + write_cr3(efi_scratch.prev_cr3); \ + __flush_tlb_all(); \ + } \ + \ __kernel_fpu_end(); \ preempt_enable(); \ __s; \ --- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c @@ -47,16 +47,7 @@ */ static u64 efi_va = EFI_VA_START;

-/* - * Scratch space used for switching the pagetable in the EFI stub - */ -struct efi_scratch { - u64 r15; - u64 prev_cr3; - pgd_t *efi_pgt; - bool use_pgd; - u64 phys_stack; -} __packed; +struct efi_scratch efi_scratch;

static void __init early_code_mapping_set_exec(int executable) { @@ -83,8 +74,11 @@ pgd_t * __init efi_call_phys_prolog(void int pgd; int n_pgds;

- if (!efi_enabled(EFI_OLD_MEMMAP)) - return NULL; + if (!efi_enabled(EFI_OLD_MEMMAP)) { + save_pgd = (pgd_t *)read_cr3(); + write_cr3((unsigned long)efi_scratch.efi_pgt); + goto out; + }

early_code_mapping_set_exec(1);

@@ -96,6 +90,7 @@ pgd_t * __init efi_call_phys_prolog(void vaddress = (unsigned long)__va(pgd * PGDIR_SIZE); set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress)); } +out: __flush_tlb_all();

return save_pgd; @@ -109,8 +104,11 @@ void __init efi_call_phys_epilog(pgd_t * int pgd_idx; int nr_pgds;

- if (!save_pgd) + if (!efi_enabled(EFI_OLD_MEMMAP)) { + write_cr3((unsigned long)save_pgd); + __flush_tlb_all(); return; + }

nr_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT) , PGDIR_SIZE);

--- a/arch/x86/platform/efi/efi_stub_64.S +++ b/arch/x86/platform/efi/efi_stub_64.S @@ -38,41 +38,6 @@ mov %rsi, %cr0; \ mov (%rsp), %rsp

- /* stolen from gcc */ - .macro FLUSH_TLB_ALL - movq %r15, efi_scratch(%rip) - movq %r14, efi_scratch+8(%rip) - movq %cr4, %r15 - movq %r15, %r14 - andb $0x7f, %r14b - movq %r14, %cr4 - movq %r15, %cr4 - movq efi_scratch+8(%rip), %r14 - movq efi_scratch(%rip), %r15 - .endm - - .macro SWITCH_PGT - cmpb $0, efi_scratch+24(%rip) - je 1f - movq %r15, efi_scratch(%rip) # r15 - # save previous CR3 - movq %cr3, %r15 - movq %r15, efi_scratch+8(%rip) # prev_cr3 - movq efi_scratch+16(%rip), %r15 # EFI pgt - movq %r15, %cr3 - 1: - .endm - - .macro RESTORE_PGT - cmpb $0, efi_scratch+24(%rip) - je 2f - movq efi_scratch+8(%rip), %r15 - movq %r15, %cr3 - movq efi_scratch(%rip), %r15 - FLUSH_TLB_ALL - 2: - .endm - ENTRY(efi_call) SAVE_XMM mov (%rsp), %rax @@ -83,16 +48,8 @@ ENTRY(efi_call) mov %r8, %r9 mov %rcx, %r8 mov %rsi, %rcx - SWITCH_PGT call *%rdi - RESTORE_PGT addq $48, %rsp RESTORE_XMM ret ENDPROC(efi_call) - - .data -ENTRY(efi_scratch) - .fill 3,8,0 - .byte 0 - .quad 0

Patches currently in stable-queue which might be from matt@codeblueprint.co.uk are

queue-4.4/x86-mm-pat-ensure-cpa-pfn-only-contains-page-frame-numbers.patch queue-4.4/x86-efi-hoist-page-table-switching-code-into-efi_call_virt.patch queue-4.4/x86-efi-build-our-own-page-table-structures.patch