[RFC PATCH 3/3] powerpc/lib: Use a temporary mm for code patching
Christopher M. Riedl
cmr at informatik.wtf
Mon Mar 23 15:52:05 AEDT 2020
Currently, code patching a STRICT_KERNEL_RWX exposes the temporary
mappings to other CPUs. These mappings should be kept local to the CPU
doing the patching. Use the pre-initialized temporary mm and patching
address for this purpose. Also add a check after patching to ensure the
patch succeeded.
Based on x86 implementation:
commit b3fd8e83ada0
("x86/alternatives: Use temporary mm for text poking")
Signed-off-by: Christopher M. Riedl <cmr at informatik.wtf>
---
arch/powerpc/lib/code-patching.c | 128 ++++++++++++++-----------------
1 file changed, 57 insertions(+), 71 deletions(-)
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 18b88ecfc5a8..f156132e8975 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -19,6 +19,7 @@
#include <asm/page.h>
#include <asm/code-patching.h>
#include <asm/setup.h>
+#include <asm/mmu_context.h>
static int __patch_instruction(unsigned int *exec_addr, unsigned int instr,
unsigned int *patch_addr)
@@ -65,99 +66,79 @@ void __init poking_init(void)
pte_unmap_unlock(ptep, ptl);
}
-static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);
-
-static int text_area_cpu_up(unsigned int cpu)
-{
- struct vm_struct *area;
-
- area = get_vm_area(PAGE_SIZE, VM_ALLOC);
- if (!area) {
- WARN_ONCE(1, "Failed to create text area for cpu %d\n",
- cpu);
- return -1;
- }
- this_cpu_write(text_poke_area, area);
-
- return 0;
-}
-
-static int text_area_cpu_down(unsigned int cpu)
-{
- free_vm_area(this_cpu_read(text_poke_area));
- return 0;
-}
-
-/*
- * Run as a late init call. This allows all the boot time patching to be done
- * simply by patching the code, and then we're called here prior to
- * mark_rodata_ro(), which happens after all init calls are run. Although
- * BUG_ON() is rude, in this case it should only happen if ENOMEM, and we judge
- * it as being preferable to a kernel that will crash later when someone tries
- * to use patch_instruction().
- */
-static int __init setup_text_poke_area(void)
-{
- BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
- "powerpc/text_poke:online", text_area_cpu_up,
- text_area_cpu_down));
-
- return 0;
-}
-late_initcall(setup_text_poke_area);
+struct patch_mapping {
+ spinlock_t *ptl; /* for protecting pte table */
+ struct temp_mm temp_mm;
+};
/*
* This can be called for kernel text or a module.
*/
-static int map_patch_area(void *addr, unsigned long text_poke_addr)
+static int map_patch(const void *addr, struct patch_mapping *patch_mapping)
{
- unsigned long pfn;
- int err;
+ struct page *page;
+ pte_t pte, *ptep;
+ pgprot_t pgprot;
if (is_vmalloc_addr(addr))
- pfn = vmalloc_to_pfn(addr);
+ page = vmalloc_to_page(addr);
else
- pfn = __pa_symbol(addr) >> PAGE_SHIFT;
+ page = virt_to_page(addr);
- err = map_kernel_page(text_poke_addr, (pfn << PAGE_SHIFT), PAGE_KERNEL);
+ if (radix_enabled())
+ pgprot = __pgprot(pgprot_val(PAGE_KERNEL));
+ else
+ pgprot = PAGE_SHARED;
- pr_devel("Mapped addr %lx with pfn %lx:%d\n", text_poke_addr, pfn, err);
- if (err)
+ ptep = get_locked_pte(patching_mm, patching_addr, &patch_mapping->ptl);
+ if (unlikely(!ptep)) {
+ pr_warn("map patch: failed to allocate pte for patching\n");
return -1;
+ }
+
+ pte = mk_pte(page, pgprot);
+ set_pte_at(patching_mm, patching_addr, ptep, pte);
+
+ init_temp_mm(&patch_mapping->temp_mm, patching_mm);
+ use_temporary_mm(&patch_mapping->temp_mm);
return 0;
}
-static inline int unmap_patch_area(unsigned long addr)
+static int unmap_patch(struct patch_mapping *patch_mapping)
{
pte_t *ptep;
pmd_t *pmdp;
pud_t *pudp;
pgd_t *pgdp;
- pgdp = pgd_offset_k(addr);
+ pgdp = pgd_offset(patching_mm, patching_addr);
if (unlikely(!pgdp))
return -EINVAL;
- pudp = pud_offset(pgdp, addr);
+ pudp = pud_offset(pgdp, patching_addr);
if (unlikely(!pudp))
return -EINVAL;
- pmdp = pmd_offset(pudp, addr);
+ pmdp = pmd_offset(pudp, patching_addr);
if (unlikely(!pmdp))
return -EINVAL;
- ptep = pte_offset_kernel(pmdp, addr);
+ ptep = pte_offset_kernel(pmdp, patching_addr);
if (unlikely(!ptep))
return -EINVAL;
- pr_devel("clearing mm %p, pte %p, addr %lx\n", &init_mm, ptep, addr);
+ /*
+ * In hash, pte_clear flushes the tlb
+ */
+ pte_clear(patching_mm, patching_addr, ptep);
+ unuse_temporary_mm(&patch_mapping->temp_mm);
/*
- * In hash, pte_clear flushes the tlb, in radix, we have to
+ * In radix, we have to explicitly flush the tlb (no-op in hash)
*/
- pte_clear(&init_mm, addr, ptep);
- flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
+ local_flush_tlb_mm(patching_mm);
+ pte_unmap_unlock(ptep, patch_mapping->ptl);
return 0;
}
@@ -167,33 +148,38 @@ static int do_patch_instruction(unsigned int *addr, unsigned int instr)
int err;
unsigned int *patch_addr = NULL;
unsigned long flags;
- unsigned long text_poke_addr;
- unsigned long kaddr = (unsigned long)addr;
+ struct patch_mapping patch_mapping;
/*
- * During early early boot patch_instruction is called
- * when text_poke_area is not ready, but we still need
- * to allow patching. We just do the plain old patching
+ * The patching_mm is initialized before calling mark_rodata_ro. Prior
+ * to this, patch_instruction is called when we don't have (and don't
+ * need) the patching_mm so just do plain old patching.
*/
- if (!this_cpu_read(text_poke_area))
+ if (!patching_mm)
return raw_patch_instruction(addr, instr);
local_irq_save(flags);
- text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr;
- if (map_patch_area(addr, text_poke_addr)) {
- err = -1;
+ err = map_patch(addr, &patch_mapping);
+ if (err)
goto out;
- }
- patch_addr = (unsigned int *)(text_poke_addr) +
- ((kaddr & ~PAGE_MASK) / sizeof(unsigned int));
+ patch_addr = (unsigned int *)(patching_addr) +
+ (offset_in_page((unsigned long)addr) /
+ sizeof(unsigned int));
__patch_instruction(addr, instr, patch_addr);
- err = unmap_patch_area(text_poke_addr);
+ err = unmap_patch(&patch_mapping);
if (err)
- pr_warn("failed to unmap %lx\n", text_poke_addr);
+ pr_warn("unmap patch: failed to unmap patch\n");
+
+ /*
+ * Something is wrong if what we just wrote doesn't match what we
+ * think we just wrote.
+ * XXX: BUG_ON() instead?
+ */
+ WARN_ON(memcmp(addr, &instr, sizeof(instr)));
out:
local_irq_restore(flags);
--
2.25.1
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