Move the EFI mixed mode return trampoline RET into .rodata, so it is
normally mapped without executable permissions. And given that this
snippet of code is really the only kernel code that we ever execute via
this 1:1 mapping, let's unmap the 1:1 mapping of the kernel .text, and
only map the page that covers the return trampoline with executable
permissions.
Note that the remainder of .rodata needs to remain mapped into the 1:1
mapping with RO/NX permissions, as literal GUIDs and strings may be
passed to the variable routines.
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---
arch/x86/platform/efi/efi_64.c | 18 +++++++++++++-----
arch/x86/platform/efi/efi_thunk_64.S | 8 +++++---
2 files changed, 18 insertions(+), 8 deletions(-)
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 1f3675453a57..b36596bf0fc3 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -176,7 +176,8 @@ virt_to_phys_or_null_size(void *va, unsigned long size)
int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
{
- unsigned long pfn, text, pf, rodata;
+ extern const u8 __efi64_thunk_ret_tramp[];
+ unsigned long pfn, text, pf, rodata, tramp;
struct page *page;
unsigned npages;
pgd_t *pgd = efi_mm.pgd;
@@ -238,11 +239,9 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
npages = (_etext - _text) >> PAGE_SHIFT;
text = __pa(_text);
- pfn = text >> PAGE_SHIFT;
- pf = _PAGE_ENC;
- if (kernel_map_pages_in_pgd(pgd, pfn, text, npages, pf)) {
- pr_err("Failed to map kernel text 1:1\n");
+ if (kernel_unmap_pages_in_pgd(pgd, text, npages)) {
+ pr_err("Failed to unmap kernel text 1:1 mapping\n");
return 1;
}
@@ -256,6 +255,15 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
return 1;
}
+ tramp = __pa(__efi64_thunk_ret_tramp);
+ pfn = tramp >> PAGE_SHIFT;
+
+ pf = _PAGE_ENC;
+ if (kernel_map_pages_in_pgd(pgd, pfn, tramp, 1, pf)) {
+ pr_err("Failed to map mixed mode return trampoline\n");
+ return 1;
+ }
+
return 0;
}
diff --git a/arch/x86/platform/efi/efi_thunk_64.S b/arch/x86/platform/efi/efi_thunk_64.S
index 4e5257a4811b..e436ce03741e 100644
--- a/arch/x86/platform/efi/efi_thunk_64.S
+++ b/arch/x86/platform/efi/efi_thunk_64.S
@@ -23,7 +23,6 @@
#include <linux/objtool.h>
#include <asm/page_types.h>
#include <asm/segment.h>
-#include <asm/nospec-branch.h>
.text
.code64
@@ -72,11 +71,14 @@ STACK_FRAME_NON_STANDARD __efi64_thunk
pushq $__KERNEL32_CS
pushq %rdi /* EFI runtime service address */
lretq
+SYM_FUNC_END(__efi64_thunk)
+ .section ".rodata", "a", @progbits
+ .balign 16
+SYM_DATA_START(__efi64_thunk_ret_tramp)
1: movq 0x20(%rsp), %rsp
pop %rbx
pop %rbp
- ANNOTATE_UNRET_SAFE
ret
int3
@@ -84,7 +86,7 @@ STACK_FRAME_NON_STANDARD __efi64_thunk
2: pushl $__KERNEL_CS
pushl %ebp
lret
-SYM_FUNC_END(__efi64_thunk)
+SYM_DATA_END(__efi64_thunk_ret_tramp)
.bss
.balign 8
--
2.35.1
