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

From: Jason Yan
Date: Wed Aug 28 2019 - 07:03:26 EST



On 2019/8/28 12:54, Scott Wood wrote:
On Fri, Aug 09, 2019 at 06:07:54PM +0800, Jason Yan wrote:
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@xxxxxxxxxx>
Cc: Diana Craciun <diana.craciun@xxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Tested-by: Diana Craciun <diana.craciun@xxxxxxx>
Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
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.

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.

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?

+/*
+ * 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.

+
+ 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
= SZ_64M" is not necessarily going to detect when you've crossed a
mapping boundary.
>> +
+ /* 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

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

.