On 2019/7/29 19:19, Christophe Leroy wrote:

Le 17/07/2019 à 10:06, Jason Yan a écrit :

quoted

The original kernel still exists in the memory, clear it now.

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Cc: Diana Craciun <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Christophe Leroy <redacted>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Kees Cook <redacted>
---
  arch/powerpc/kernel/kaslr_booke.c  | 11 +++++++++++
  arch/powerpc/mm/mmu_decl.h         |  2 ++
  arch/powerpc/mm/nohash/fsl_booke.c |  1 +
  3 files changed, 14 insertions(+)

diff --git a/arch/powerpc/kernel/kaslr_booke.c 

b/arch/powerpc/kernel/kaslr_booke.c
index 90357f4bd313..00339c05879f 100644

--- a/arch/powerpc/kernel/kaslr_booke.c
+++ b/arch/powerpc/kernel/kaslr_booke.c

@@ -412,3 +412,14 @@ notrace void __init kaslr_early_init(void 

*dt_ptr, phys_addr_t size)
      reloc_kernel_entry(dt_ptr, kimage_vaddr);
  }
+
+void __init kaslr_second_init(void)
+{
+    /* If randomized, clear the original kernel */
+    if (kimage_vaddr != KERNELBASE) {
+        unsigned long kernel_sz;
+
+        kernel_sz = (unsigned long)_end - kimage_vaddr;
+        memset((void *)KERNELBASE, 0, kernel_sz);

Why are we clearing ? Is that just to tidy up or is it of security 
importance ?

If we leave it there, attackers can still find the kernel object very
easy, it's still dangerous especially if without 
CONFIG_STRICT_KERNEL_RWX enabled.

If so, maybe memzero_explicit() should be used instead ?

OK

quoted

+    }
+}

diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
index 754ae1e69f92..9912ee598f9b 100644
--- a/arch/powerpc/mm/mmu_decl.h
+++ b/arch/powerpc/mm/mmu_decl.h

@@ -150,8 +150,10 @@ extern void loadcam_multi(int first_idx, int num, 

int tmp_idx);
  #ifdef CONFIG_RANDOMIZE_BASE
  extern void kaslr_early_init(void *dt_ptr, phys_addr_t size);
+extern void kaslr_second_init(void);

No new 'extern' please.

quoted

  #else
  static inline void kaslr_early_init(void *dt_ptr, phys_addr_t size) {}
+static inline void kaslr_second_init(void) {}
  #endif
  struct tlbcam {

diff --git a/arch/powerpc/mm/nohash/fsl_booke.c 

b/arch/powerpc/mm/nohash/fsl_booke.c
index 8d25a8dc965f..fa5a87f5c08e 100644

--- a/arch/powerpc/mm/nohash/fsl_booke.c
+++ b/arch/powerpc/mm/nohash/fsl_booke.c

@@ -269,6 +269,7 @@ notrace void __init relocate_init(u64 dt_ptr, 

phys_addr_t start)
      kernstart_addr = start;
      if (is_second_reloc) {
          virt_phys_offset = PAGE_OFFSET - memstart_addr;
+        kaslr_second_init();
          return;
      }

Christophe

.