Re: [PATCH v6 06/12] powerpc/fsl_booke/32: implement KASLR infrastructure

On 2019/8/28 12:54, Scott Wood wrote:

On Fri, Aug 09, 2019 at 06:07:54PM +0800, Jason Yan wrote:

quoted

This patch add support to boot kernel from places other than KERNELBASE.
Since CONFIG_RELOCATABLE has already supported, what we need to do is
map or copy kernel to a proper place and relocate. Freescale Book-E
parts expect lowmem to be mapped by fixed TLB entries(TLB1). The TLB1
entries are not suitable to map the kernel directly in a randomized
region, so we chose to copy the kernel to a proper place and restart to
relocate.

The offset of the kernel was not randomized yet(a fixed 64M is set). We
will randomize it in the next patch.

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>
Tested-by: Diana Craciun <redacted>
Reviewed-by: Christophe Leroy <redacted>
---
  arch/powerpc/Kconfig                          | 11 ++++
  arch/powerpc/kernel/Makefile                  |  1 +
  arch/powerpc/kernel/early_32.c                |  2 +-
  arch/powerpc/kernel/fsl_booke_entry_mapping.S | 17 +++--
  arch/powerpc/kernel/head_fsl_booke.S          | 13 +++-
  arch/powerpc/kernel/kaslr_booke.c             | 62 +++++++++++++++++++
  arch/powerpc/mm/mmu_decl.h                    |  7 +++
  arch/powerpc/mm/nohash/fsl_booke.c            |  7 ++-
  8 files changed, 105 insertions(+), 15 deletions(-)
  create mode 100644 arch/powerpc/kernel/kaslr_booke.c

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 77f6ebf97113..710c12ef7159 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig

@@ -548,6 +548,17 @@ config RELOCATABLE
  	  setting can still be useful to bootwrappers that need to know the
  	  load address of the kernel (eg. u-boot/mkimage).
  
+config RANDOMIZE_BASE
+	bool "Randomize the address of the kernel image"
+	depends on (FSL_BOOKE && FLATMEM && PPC32)
+	depends on RELOCATABLE
+	help
+	  Randomizes the virtual address at which the kernel image is
+	  loaded, as a security feature that deters exploit attempts
+	  relying on knowledge of the location of kernel internals.
+
+	  If unsure, say N.
+

Why is N the safe default (other than concerns about code maturity,
though arm64 and mips don't seem to have updated this recommendation
after several years)?  On x86 this defaults to Y.

Actually I would like to set this default Y. I was just wondering if
people like this feature or not at the beginning so I had to be more
careful.

quoted

diff --git a/arch/powerpc/kernel/fsl_booke_entry_mapping.S b/arch/powerpc/kernel/fsl_booke_entry_mapping.S
index f4d3eaae54a9..641920d4f694 100644
--- a/arch/powerpc/kernel/fsl_booke_entry_mapping.S
+++ b/arch/powerpc/kernel/fsl_booke_entry_mapping.S

@@ -155,23 +155,22 @@ skpinv:	addi	r6,r6,1				/* Increment */
  
  #if defined(ENTRY_MAPPING_BOOT_SETUP)
  
-/* 6. Setup KERNELBASE mapping in TLB1[0] */
+/* 6. Setup kernstart_virt_addr mapping in TLB1[0] */
  	lis	r6,0x1000		/* Set MAS0(TLBSEL) = TLB1(1), ESEL = 0 */
  	mtspr	SPRN_MAS0,r6
  	lis	r6,(MAS1_VALID|MAS1_IPROT)@h
  	ori	r6,r6,(MAS1_TSIZE(BOOK3E_PAGESZ_64M))@l
  	mtspr	SPRN_MAS1,r6
-	lis	r6,MAS2_VAL(PAGE_OFFSET, BOOK3E_PAGESZ_64M, MAS2_M_IF_NEEDED)@h
-	ori	r6,r6,MAS2_VAL(PAGE_OFFSET, BOOK3E_PAGESZ_64M, MAS2_M_IF_NEEDED)@l
-	mtspr	SPRN_MAS2,r6
+	lis     r6,MAS2_EPN_MASK(BOOK3E_PAGESZ_64M)@h
+	ori     r6,r6,MAS2_EPN_MASK(BOOK3E_PAGESZ_64M)@l
+	and     r6,r6,r20
+	ori	r6,r6,MAS2_M_IF_NEEDED@l
+	mtspr   SPRN_MAS2,r6

Please use tabs rather than spaces between the mnemonic and the
arguments.

It looks like that was the last user of MAS2_VAL so let's remove it.

OK.

quoted

diff --git a/arch/powerpc/kernel/kaslr_booke.c b/arch/powerpc/kernel/kaslr_booke.c
new file mode 100644
index 000000000000..f8dc60534ac1
--- /dev/null
+++ b/arch/powerpc/kernel/kaslr_booke.c

Shouldn't this go under arch/powerpc/mm/nohash?

quoted

+/*
+ * To see if we need to relocate the kernel to a random offset
+ * void *dt_ptr - address of the device tree
+ * phys_addr_t size - size of the first memory block
+ */
+notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
+{
+	unsigned long tlb_virt;
+	phys_addr_t tlb_phys;
+	unsigned long offset;
+	unsigned long kernel_sz;
+
+	kernel_sz = (unsigned long)_end - KERNELBASE;

Why KERNELBASE and not kernstart_addr?

Did you mean kernstart_virt_addr? It should be kernstart_virt_addr.

quoted

+
+	offset = kaslr_choose_location(dt_ptr, size, kernel_sz);
+
+	if (offset == 0)
+		return;
+
+	kernstart_virt_addr += offset;
+	kernstart_addr += offset;
+
+	is_second_reloc = 1;
+
+	if (offset >= SZ_64M) {
+		tlb_virt = round_down(kernstart_virt_addr, SZ_64M);
+		tlb_phys = round_down(kernstart_addr, SZ_64M);

If kernstart_addr wasn't 64M-aligned before adding offset, then "offset

quoted

= SZ_64M" is not necessarily going to detect when you've crossed a

mapping boundary.

quoted

quoted

+

+		/* Create kernel map to relocate in */
+		create_tlb_entry(tlb_phys, tlb_virt, 1);
+	}
+
+	/* Copy the kernel to it's new location and run */
+	memcpy((void *)kernstart_virt_addr, (void *)KERNELBASE, kernel_sz);
+
+	reloc_kernel_entry(dt_ptr, kernstart_virt_addr);
+}

After copying, call flush_icache_range() on the destination.

OK

quoted

diff --git a/arch/powerpc/mm/nohash/fsl_booke.c b/arch/powerpc/mm/nohash/fsl_booke.c
index 556e3cd52a35..2dc27cf88add 100644
--- a/arch/powerpc/mm/nohash/fsl_booke.c
+++ b/arch/powerpc/mm/nohash/fsl_booke.c

@@ -263,7 +263,8 @@ void setup_initial_memory_limit(phys_addr_t first_memblock_base,
  int __initdata is_second_reloc;
  notrace void __init relocate_init(u64 dt_ptr, phys_addr_t start)
  {
-	unsigned long base = KERNELBASE;
+	unsigned long base = kernstart_virt_addr;
+	phys_addr_t size;
  
  	kernstart_addr = start;
  	if (is_second_reloc) {

@@ -291,7 +292,7 @@ notrace void __init relocate_init(u64 dt_ptr, phys_addr_t start)
  	start &= ~0x3ffffff;
  	base &= ~0x3ffffff;
  	virt_phys_offset = base - start;
-	early_get_first_memblock_info(__va(dt_ptr), NULL);
+	early_get_first_memblock_info(__va(dt_ptr), &size);
  	/*
  	 * We now get the memstart_addr, then we should check if this
  	 * address is the same as what the PAGE_OFFSET map to now. If

@@ -316,6 +317,8 @@ notrace void __init relocate_init(u64 dt_ptr, phys_addr_t start)
  		/* We should never reach here */
  		panic("Relocation error");
  	}
+
+	kaslr_early_init(__va(dt_ptr), size);

Are you assuming that available memory starts at physical address zero?
This isn't true of some partitioning scenarios, or in a kdump crash
kernel.

I'm not assuming that but I haven't tested that case for now. I will 
reconsider and test these scenarios and fix all bugs.

-Scott

.