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author | Baoquan He <bhe@redhat.com> | 2017-05-26 12:36:50 +0100 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2017-05-28 11:06:16 +0200 |
commit | 94133e46a0f5ca3f138479806104ab4a8cb0455e (patch) | |
tree | 8159e0fd072d0b496f2dd5ebe825ceb44d449aa9 /arch/x86 | |
parent | 4e52797d2efefac3271abdc54439a3435abd77b9 (diff) | |
download | linux-94133e46a0f5ca3f138479806104ab4a8cb0455e.tar.gz linux-94133e46a0f5ca3f138479806104ab4a8cb0455e.tar.bz2 linux-94133e46a0f5ca3f138479806104ab4a8cb0455e.zip |
x86/efi: Correct EFI identity mapping under 'efi=old_map' when KASLR is enabled
For EFI with the 'efi=old_map' kernel option specified, the kernel will panic
when KASLR is enabled:
BUG: unable to handle kernel paging request at 000000007febd57e
IP: 0x7febd57e
PGD 1025a067
PUD 0
Oops: 0010 [#1] SMP
Call Trace:
efi_enter_virtual_mode()
start_kernel()
x86_64_start_reservations()
x86_64_start_kernel()
start_cpu()
The root cause is that the identity mapping is not built correctly
in the 'efi=old_map' case.
On 'nokaslr' kernels, PAGE_OFFSET is 0xffff880000000000 which is PGDIR_SIZE
aligned. We can borrow the PUD table from the direct mappings safely. Given a
physical address X, we have pud_index(X) == pud_index(__va(X)).
However, on KASLR kernels, PAGE_OFFSET is PUD_SIZE aligned. For a given physical
address X, pud_index(X) != pud_index(__va(X)). We can't just copy the PGD entry
from direct mapping to build identity mapping, instead we need to copy the
PUD entries one by one from the direct mapping.
Fix it.
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Bhupesh Sharma <bhsharma@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Young <dyoung@redhat.com>
Cc: Frank Ramsay <frank.ramsay@hpe.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russ Anderson <rja@sgi.com>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170526113652.21339-5-matt@codeblueprint.co.uk
[ Fixed and reworded the changelog and code comments to be more readable. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86')
-rw-r--r-- | arch/x86/platform/efi/efi_64.c | 79 |
1 files changed, 71 insertions, 8 deletions
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c index c488625c9712..eb8dff15a7f6 100644 --- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c @@ -71,11 +71,13 @@ static void __init early_code_mapping_set_exec(int executable) pgd_t * __init efi_call_phys_prolog(void) { - unsigned long vaddress; - pgd_t *save_pgd; + unsigned long vaddr, addr_pgd, addr_p4d, addr_pud; + pgd_t *save_pgd, *pgd_k, *pgd_efi; + p4d_t *p4d, *p4d_k, *p4d_efi; + pud_t *pud; int pgd; - int n_pgds; + int n_pgds, i, j; if (!efi_enabled(EFI_OLD_MEMMAP)) { save_pgd = (pgd_t *)read_cr3(); @@ -88,10 +90,49 @@ pgd_t * __init efi_call_phys_prolog(void) n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT), PGDIR_SIZE); save_pgd = kmalloc_array(n_pgds, sizeof(*save_pgd), GFP_KERNEL); + /* + * Build 1:1 identity mapping for efi=old_map usage. Note that + * PAGE_OFFSET is PGDIR_SIZE aligned when KASLR is disabled, while + * it is PUD_SIZE ALIGNED with KASLR enabled. So for a given physical + * address X, the pud_index(X) != pud_index(__va(X)), we can only copy + * PUD entry of __va(X) to fill in pud entry of X to build 1:1 mapping. + * This means here we can only reuse the PMD tables of the direct mapping. + */ for (pgd = 0; pgd < n_pgds; pgd++) { - save_pgd[pgd] = *pgd_offset_k(pgd * PGDIR_SIZE); - vaddress = (unsigned long)__va(pgd * PGDIR_SIZE); - set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress)); + addr_pgd = (unsigned long)(pgd * PGDIR_SIZE); + vaddr = (unsigned long)__va(pgd * PGDIR_SIZE); + pgd_efi = pgd_offset_k(addr_pgd); + save_pgd[pgd] = *pgd_efi; + + p4d = p4d_alloc(&init_mm, pgd_efi, addr_pgd); + if (!p4d) { + pr_err("Failed to allocate p4d table!\n"); + goto out; + } + + for (i = 0; i < PTRS_PER_P4D; i++) { + addr_p4d = addr_pgd + i * P4D_SIZE; + p4d_efi = p4d + p4d_index(addr_p4d); + + pud = pud_alloc(&init_mm, p4d_efi, addr_p4d); + if (!pud) { + pr_err("Failed to allocate pud table!\n"); + goto out; + } + + for (j = 0; j < PTRS_PER_PUD; j++) { + addr_pud = addr_p4d + j * PUD_SIZE; + + if (addr_pud > (max_pfn << PAGE_SHIFT)) + break; + + vaddr = (unsigned long)__va(addr_pud); + + pgd_k = pgd_offset_k(vaddr); + p4d_k = p4d_offset(pgd_k, vaddr); + pud[j] = *pud_offset(p4d_k, vaddr); + } + } } out: __flush_tlb_all(); @@ -104,8 +145,11 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd) /* * After the lock is released, the original page table is restored. */ - int pgd_idx; + int pgd_idx, i; int nr_pgds; + pgd_t *pgd; + p4d_t *p4d; + pud_t *pud; if (!efi_enabled(EFI_OLD_MEMMAP)) { write_cr3((unsigned long)save_pgd); @@ -115,9 +159,28 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd) nr_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT) , PGDIR_SIZE); - for (pgd_idx = 0; pgd_idx < nr_pgds; pgd_idx++) + for (pgd_idx = 0; pgd_idx < nr_pgds; pgd_idx++) { + pgd = pgd_offset_k(pgd_idx * PGDIR_SIZE); set_pgd(pgd_offset_k(pgd_idx * PGDIR_SIZE), save_pgd[pgd_idx]); + if (!(pgd_val(*pgd) & _PAGE_PRESENT)) + continue; + + for (i = 0; i < PTRS_PER_P4D; i++) { + p4d = p4d_offset(pgd, + pgd_idx * PGDIR_SIZE + i * P4D_SIZE); + + if (!(p4d_val(*p4d) & _PAGE_PRESENT)) + continue; + + pud = (pud_t *)p4d_page_vaddr(*p4d); + pud_free(&init_mm, pud); + } + + p4d = (p4d_t *)pgd_page_vaddr(*pgd); + p4d_free(&init_mm, p4d); + } + kfree(save_pgd); __flush_tlb_all(); |