[PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with %cr3

Sai Praneeth Prakhya
2017-12-17T00:06:42Z

From: Sai Praneeth <sai.praneeth.prakhya-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

Use helper function (efi_switch_mm()) to switch to/from efi_mm. We
switch to efi_mm before calling
1. efi_set_virtual_address_map() and
2. Invoking any efi_runtime_service()

Likewise, we need to switch back to previous mm (mm context stolen by
efi_mm) after the above calls return successfully. We can use
efi_switch_mm() helper function only with x86_64 kernel and
"efi=old_map" disabled because, x86_32 and efi=old_map doesn't use
efi_pgd, rather they use swapper_pg_dir.

Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Lee, Chun-Yi <jlee-IBi9RG/b67k@public.gmane.org>
Cc: Borislav Petkov <bp-Gina5bIWoIWzQB+pC5nmwQ@public.gmane.org>
Cc: Tony Luck <tony.luck-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Michael S. Tsirkin <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Bhupesh Sharma <bhsharma-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Ricardo Neri <ricardo.neri-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Matt Fleming <matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org>
Cc: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Cc: Ravi Shankar <ravi.v.shankar-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Tested-by: Bhupesh Sharma <bhsharma-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
arch/x86/include/asm/efi.h | 25 +++++++++-------------
arch/x86/platform/efi/efi_64.c | 41 ++++++++++++++++++------------------
arch/x86/platform/efi/efi_thunk_64.S | 2 +-
3 files changed, 32 insertions(+), 36 deletions(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 00f977ddd718..cda9940bed7a 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -62,14 +62,13 @@ extern asmlinkage u64 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 - Scratch space used while switching to/from efi_mm
+ * @phys_stack: stack used during EFI Mixed Mode
+ * @prev_mm: store/restore stolen mm_struct while switching to/from efi_mm
*/
struct efi_scratch {
- u64 r15;
- u64 prev_cr3;
- pgd_t *efi_pgt;
- bool use_pgd;
- u64 phys_stack;
+ u64 phys_stack;
+ struct mm_struct *prev_mm;
} __packed;

#define arch_efi_call_virt_setup() \
@@ -78,11 +77,8 @@ struct efi_scratch {
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(); \
- } \
+ if (!efi_enabled(EFI_OLD_MEMMAP)) \
+ efi_switch_mm(&efi_mm); \
})

#define arch_efi_call_virt(p, f, args...) \
@@ -90,10 +86,8 @@ struct efi_scratch {

#define arch_efi_call_virt_teardown() \
({ \
- if (efi_scratch.use_pgd) { \
- write_cr3(efi_scratch.prev_cr3); \
- __flush_tlb_all(); \
- } \
+ if (!efi_enabled(EFI_OLD_MEMMAP)) \
+ efi_switch_mm(efi_scratch.prev_mm); \
\
__kernel_fpu_end(); \
preempt_enable(); \
@@ -135,6 +129,7 @@ extern void __init efi_dump_pagetable(void);
extern void __init efi_apply_memmap_quirks(void);
extern int __init efi_reuse_config(u64 tables, int nr_tables);
extern void efi_delete_dummy_variable(void);
+extern void efi_switch_mm(struct mm_struct *mm);

struct efi_setup_data {
u64 fw_vendor;
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 6b541bdbda5f..c325b1cc4d1a 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -82,9 +82,8 @@ pgd_t * __init efi_call_phys_prolog(void)
int n_pgds, i, j;

if (!efi_enabled(EFI_OLD_MEMMAP)) {
- save_pgd = (pgd_t *)__read_cr3();
- write_cr3((unsigned long)efi_scratch.efi_pgt);
- goto out;
+ efi_switch_mm(&efi_mm);
+ return NULL;
}

early_code_mapping_set_exec(1);
@@ -154,8 +153,7 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
pud_t *pud;

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

@@ -341,13 +339,6 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
return 0;

/*
- * Since the PGD is encrypted, set the encryption mask so that when
- * this value is loaded into cr3 the PGD will be decrypted during
- * the pagetable walk.
- */
- efi_scratch.efi_pgt = (pgd_t *)__sme_pa(pgd);
-
- /*
* It can happen that the physical address of new_memmap lands in memory
* which is not mapped in the EFI page table. Therefore we need to go
* and ident-map those pages containing the map before calling
@@ -360,8 +351,6 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
return 1;
}

- efi_scratch.use_pgd = true;
-
/*
* Certain firmware versions are way too sentimential and still believe
* they are exclusive and unquestionable owners of the first physical page,
@@ -620,6 +609,22 @@ void __init efi_dump_pagetable(void)
#endif
}

+/*
+ * Makes the calling thread switch to/from efi_mm context. Can be used
+ * for SetVirtualAddressMap() i.e. current->active_mm == init_mm as well
+ * as during efi runtime calls i.e current->active_mm == current_mm.
+ * We are not mm_dropping()/mm_grabbing() any mm, because we are not
+ * losing/creating any references.
+ */
+void efi_switch_mm(struct mm_struct *mm)
+{
+ task_lock(current);
+ efi_scratch.prev_mm = current->active_mm;
+ current->active_mm = mm;
+ switch_mm(efi_scratch.prev_mm, mm, NULL);
+ task_unlock(current);
+}
+
#ifdef CONFIG_EFI_MIXED
extern efi_status_t efi64_thunk(u32, ...);

@@ -673,17 +678,13 @@ efi_status_t efi_thunk_set_virtual_address_map(
efi_sync_low_kernel_mappings();
local_irq_save(flags);

- efi_scratch.prev_cr3 = __read_cr3();
- write_cr3((unsigned long)efi_scratch.efi_pgt);
- __flush_tlb_all();
+ efi_switch_mm(&efi_mm);

func = (u32)(unsigned long)phys_set_virtual_address_map;
status = efi64_thunk(func, memory_map_size, descriptor_size,
descriptor_version, virtual_map);

- write_cr3(efi_scratch.prev_cr3);
- __flush_tlb_all();
- local_irq_restore(flags);
+ efi_switch_mm(efi_scratch.prev_mm);

return status;
}
diff --git a/arch/x86/platform/efi/efi_thunk_64.S b/arch/x86/platform/efi/efi_thunk_64.S
index 189b218da87c..46c58b08739c 100644
--- a/arch/x86/platform/efi/efi_thunk_64.S
+++ b/arch/x86/platform/efi/efi_thunk_64.S
@@ -33,7 +33,7 @@ ENTRY(efi64_thunk)
* Switch to 1:1 mapped 32-bit stack pointer.
*/
movq %rsp, efi_saved_sp(%rip)
- movq efi_scratch+25(%rip), %rsp
+ movq efi_scratch(%rip), %rsp

/*
* Calculate the physical address of the kernel text.
--
2.1.4