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

From: Jason Yan
Date: Thu Aug 29 2019 - 02:27:11 EST

On 2019/8/28 13:47, Christophe Leroy wrote:

Le 28/08/2019 Ã 06:54, Scott Wood a ÃcritÂ:
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

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/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)
+ÂÂÂ unsigned long tlb_virt;
+ÂÂÂ phys_addr_t tlb_phys;
+ÂÂÂ unsigned long offset;
+ÂÂÂ unsigned long kernel_sz;
+ÂÂÂ kernel_sz = (unsigned long)_end - KERNELBASE;

Why KERNELBASE and not kernstart_addr?

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

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

After copying, call flush_icache_range() on the destination.

Function copy_and_flush() does the copy and the flush. I think it should be used instead of memcpy() + flush_icache_range()

Hi Christophe,

Thanks for the suggestion. But I think copy_and_flush() is not included in fsl booke code, maybe move this function to misc.S?