summaryrefslogtreecommitdiffstats
path: root/arch/x86/kernel/alternative.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/x86/kernel/alternative.c')
-rw-r--r--arch/x86/kernel/alternative.c201
1 files changed, 154 insertions, 47 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 9a79c7808f9c..7b9b49dfc05a 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -12,6 +12,7 @@
#include <linux/slab.h>
#include <linux/kdebug.h>
#include <linux/kprobes.h>
+#include <linux/mmu_context.h>
#include <asm/text-patching.h>
#include <asm/alternative.h>
#include <asm/sections.h>
@@ -264,7 +265,7 @@ static void __init_or_module add_nops(void *insns, unsigned int len)
extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
extern s32 __smp_locks[], __smp_locks_end[];
-void *text_poke_early(void *addr, const void *opcode, size_t len);
+void text_poke_early(void *addr, const void *opcode, size_t len);
/*
* Are we looking at a near JMP with a 1 or 4-byte displacement.
@@ -666,16 +667,136 @@ void __init alternative_instructions(void)
* instructions. And on the local CPU you need to be protected again NMI or MCE
* handlers seeing an inconsistent instruction while you patch.
*/
-void *__init_or_module text_poke_early(void *addr, const void *opcode,
- size_t len)
+void __init_or_module text_poke_early(void *addr, const void *opcode,
+ size_t len)
{
unsigned long flags;
+
+ if (boot_cpu_has(X86_FEATURE_NX) &&
+ is_module_text_address((unsigned long)addr)) {
+ /*
+ * Modules text is marked initially as non-executable, so the
+ * code cannot be running and speculative code-fetches are
+ * prevented. Just change the code.
+ */
+ memcpy(addr, opcode, len);
+ } else {
+ local_irq_save(flags);
+ memcpy(addr, opcode, len);
+ local_irq_restore(flags);
+ sync_core();
+
+ /*
+ * Could also do a CLFLUSH here to speed up CPU recovery; but
+ * that causes hangs on some VIA CPUs.
+ */
+ }
+}
+
+__ro_after_init struct mm_struct *poking_mm;
+__ro_after_init unsigned long poking_addr;
+
+static void *__text_poke(void *addr, const void *opcode, size_t len)
+{
+ bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE;
+ struct page *pages[2] = {NULL};
+ temp_mm_state_t prev;
+ unsigned long flags;
+ pte_t pte, *ptep;
+ spinlock_t *ptl;
+ pgprot_t pgprot;
+
+ /*
+ * While boot memory allocator is running we cannot use struct pages as
+ * they are not yet initialized. There is no way to recover.
+ */
+ BUG_ON(!after_bootmem);
+
+ if (!core_kernel_text((unsigned long)addr)) {
+ pages[0] = vmalloc_to_page(addr);
+ if (cross_page_boundary)
+ pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
+ } else {
+ pages[0] = virt_to_page(addr);
+ WARN_ON(!PageReserved(pages[0]));
+ if (cross_page_boundary)
+ pages[1] = virt_to_page(addr + PAGE_SIZE);
+ }
+ /*
+ * If something went wrong, crash and burn since recovery paths are not
+ * implemented.
+ */
+ BUG_ON(!pages[0] || (cross_page_boundary && !pages[1]));
+
local_irq_save(flags);
- memcpy(addr, opcode, len);
+
+ /*
+ * Map the page without the global bit, as TLB flushing is done with
+ * flush_tlb_mm_range(), which is intended for non-global PTEs.
+ */
+ pgprot = __pgprot(pgprot_val(PAGE_KERNEL) & ~_PAGE_GLOBAL);
+
+ /*
+ * The lock is not really needed, but this allows to avoid open-coding.
+ */
+ ptep = get_locked_pte(poking_mm, poking_addr, &ptl);
+
+ /*
+ * This must not fail; preallocated in poking_init().
+ */
+ VM_BUG_ON(!ptep);
+
+ pte = mk_pte(pages[0], pgprot);
+ set_pte_at(poking_mm, poking_addr, ptep, pte);
+
+ if (cross_page_boundary) {
+ pte = mk_pte(pages[1], pgprot);
+ set_pte_at(poking_mm, poking_addr + PAGE_SIZE, ptep + 1, pte);
+ }
+
+ /*
+ * Loading the temporary mm behaves as a compiler barrier, which
+ * guarantees that the PTE will be set at the time memcpy() is done.
+ */
+ prev = use_temporary_mm(poking_mm);
+
+ kasan_disable_current();
+ memcpy((u8 *)poking_addr + offset_in_page(addr), opcode, len);
+ kasan_enable_current();
+
+ /*
+ * Ensure that the PTE is only cleared after the instructions of memcpy
+ * were issued by using a compiler barrier.
+ */
+ barrier();
+
+ pte_clear(poking_mm, poking_addr, ptep);
+ if (cross_page_boundary)
+ pte_clear(poking_mm, poking_addr + PAGE_SIZE, ptep + 1);
+
+ /*
+ * Loading the previous page-table hierarchy requires a serializing
+ * instruction that already allows the core to see the updated version.
+ * Xen-PV is assumed to serialize execution in a similar manner.
+ */
+ unuse_temporary_mm(prev);
+
+ /*
+ * Flushing the TLB might involve IPIs, which would require enabled
+ * IRQs, but not if the mm is not used, as it is in this point.
+ */
+ flush_tlb_mm_range(poking_mm, poking_addr, poking_addr +
+ (cross_page_boundary ? 2 : 1) * PAGE_SIZE,
+ PAGE_SHIFT, false);
+
+ /*
+ * If the text does not match what we just wrote then something is
+ * fundamentally screwy; there's nothing we can really do about that.
+ */
+ BUG_ON(memcmp(addr, opcode, len));
+
+ pte_unmap_unlock(ptep, ptl);
local_irq_restore(flags);
- sync_core();
- /* Could also do a CLFLUSH here to speed up CPU recovery; but
- that causes hangs on some VIA CPUs. */
return addr;
}
@@ -689,48 +810,36 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode,
* It means the size must be writable atomically and the address must be aligned
* in a way that permits an atomic write. It also makes sure we fit on a single
* page.
+ *
+ * Note that the caller must ensure that if the modified code is part of a
+ * module, the module would not be removed during poking. This can be achieved
+ * by registering a module notifier, and ordering module removal and patching
+ * trough a mutex.
*/
void *text_poke(void *addr, const void *opcode, size_t len)
{
- unsigned long flags;
- char *vaddr;
- struct page *pages[2];
- int i;
-
- /*
- * While boot memory allocator is runnig we cannot use struct
- * pages as they are not yet initialized.
- */
- BUG_ON(!after_bootmem);
-
lockdep_assert_held(&text_mutex);
- if (!core_kernel_text((unsigned long)addr)) {
- pages[0] = vmalloc_to_page(addr);
- pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
- } else {
- pages[0] = virt_to_page(addr);
- WARN_ON(!PageReserved(pages[0]));
- pages[1] = virt_to_page(addr + PAGE_SIZE);
- }
- BUG_ON(!pages[0]);
- local_irq_save(flags);
- set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0]));
- if (pages[1])
- set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1]));
- vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0);
- memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
- clear_fixmap(FIX_TEXT_POKE0);
- if (pages[1])
- clear_fixmap(FIX_TEXT_POKE1);
- local_flush_tlb();
- sync_core();
- /* Could also do a CLFLUSH here to speed up CPU recovery; but
- that causes hangs on some VIA CPUs. */
- for (i = 0; i < len; i++)
- BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
- local_irq_restore(flags);
- return addr;
+ return __text_poke(addr, opcode, len);
+}
+
+/**
+ * text_poke_kgdb - Update instructions on a live kernel by kgdb
+ * @addr: address to modify
+ * @opcode: source of the copy
+ * @len: length to copy
+ *
+ * Only atomic text poke/set should be allowed when not doing early patching.
+ * It means the size must be writable atomically and the address must be aligned
+ * in a way that permits an atomic write. It also makes sure we fit on a single
+ * page.
+ *
+ * Context: should only be used by kgdb, which ensures no other core is running,
+ * despite the fact it does not hold the text_mutex.
+ */
+void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
+{
+ return __text_poke(addr, opcode, len);
}
static void do_sync_core(void *info)
@@ -788,7 +897,7 @@ NOKPROBE_SYMBOL(poke_int3_handler);
* replacing opcode
* - sync cores
*/
-void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
+void text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
{
unsigned char int3 = 0xcc;
@@ -830,7 +939,5 @@ void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
* the writing of the new instruction.
*/
bp_patching_in_progress = false;
-
- return addr;
}