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Subject[tip: x86/seves] x86/boot/compressed/64: Always switch to own page table
The following commit has been merged into the x86/seves branch of tip:

Commit-ID: ca0e22d4f011a56e974fa3a712d76e86a791559d
Gitweb: https://git.kernel.org/tip/ca0e22d4f011a56e974fa3a712d76e86a791559d
Author: Joerg Roedel <jroedel@suse.de>
AuthorDate: Mon, 07 Sep 2020 15:15:17 +02:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 07 Sep 2020 19:45:25 +02:00

x86/boot/compressed/64: Always switch to own page table

When booted through startup_64(), the kernel keeps running on the EFI
page table until the KASLR code sets up its own page table. Without
KASLR, the pre-decompression boot code never switches off the EFI page
table. Change that by unconditionally switching to a kernel-controlled
page table after relocation.

This makes sure the kernel can make changes to the mapping when
necessary, for example map pages unencrypted in SEV and SEV-ES guests.

Also, remove the debug_putstr() calls in initialize_identity_maps()
because the function now runs before console_init() is called.

[ bp: Massage commit message. ]

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200907131613.12703-17-joro@8bytes.org
---
arch/x86/boot/compressed/head_64.S | 3 +-
arch/x86/boot/compressed/ident_map_64.c | 51 ++++++++++++++----------
arch/x86/boot/compressed/kaslr.c | 3 +-
3 files changed, 32 insertions(+), 25 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index c634ed8..fb6c039 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -543,10 +543,11 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
rep stosq

/*
- * Load stage2 IDT
+ * Load stage2 IDT and switch to our own page-table
*/
pushq %rsi
call load_stage2_idt
+ call initialize_identity_maps
popq %rsi

/*
diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index e3d980a..ecf9353 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -86,9 +86,31 @@ phys_addr_t physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
*/
static struct x86_mapping_info mapping_info;

+/*
+ * Adds the specified range to what will become the new identity mappings.
+ * Once all ranges have been added, the new mapping is activated by calling
+ * finalize_identity_maps() below.
+ */
+void add_identity_map(unsigned long start, unsigned long size)
+{
+ unsigned long end = start + size;
+
+ /* Align boundary to 2M. */
+ start = round_down(start, PMD_SIZE);
+ end = round_up(end, PMD_SIZE);
+ if (start >= end)
+ return;
+
+ /* Build the mapping. */
+ kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt,
+ start, end);
+}
+
/* Locates and clears a region for a new top level page table. */
void initialize_identity_maps(void)
{
+ unsigned long start, size;
+
/* If running as an SEV guest, the encryption mask is required. */
set_sev_encryption_mask();

@@ -121,37 +143,24 @@ void initialize_identity_maps(void)
*/
top_level_pgt = read_cr3_pa();
if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {
- debug_putstr("booted via startup_32()\n");
pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
} else {
- debug_putstr("booted via startup_64()\n");
pgt_data.pgt_buf = _pgtable;
pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);
}
-}

-/*
- * Adds the specified range to what will become the new identity mappings.
- * Once all ranges have been added, the new mapping is activated by calling
- * finalize_identity_maps() below.
- */
-void add_identity_map(unsigned long start, unsigned long size)
-{
- unsigned long end = start + size;
-
- /* Align boundary to 2M. */
- start = round_down(start, PMD_SIZE);
- end = round_up(end, PMD_SIZE);
- if (start >= end)
- return;
-
- /* Build the mapping. */
- kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt,
- start, end);
+ /*
+ * New page-table is set up - map the kernel image and load it
+ * into cr3.
+ */
+ start = (unsigned long)_head;
+ size = _end - _head;
+ add_identity_map(start, size);
+ write_cr3(top_level_pgt);
}

/*
diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index e27de98..8266286 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -861,9 +861,6 @@ void choose_random_location(unsigned long input,

boot_params->hdr.loadflags |= KASLR_FLAG;

- /* Prepare to add new identity pagetables on demand. */
- initialize_identity_maps();
-
if (IS_ENABLED(CONFIG_X86_32))
mem_limit = KERNEL_IMAGE_SIZE;
else
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