[RFC PATCH 0/4] Fix page permission on arm64 architectures
Ilias Apalodimas
ilias.apalodimas at linaro.org
Fri Feb 14 14:32:09 CET 2025
On Sun, 9 Feb 2025 at 16:28, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Ilias,
>
> On Thu, 6 Feb 2025 at 05:40, Ilias Apalodimas
> <ilias.apalodimas at linaro.org> wrote:
> >
> > Hi Simon,
> >
> > On Thu, 6 Feb 2025 at 14:33, Simon Glass <sjg at chromium.org> wrote:
> > >
> > > Hi Ilias,
> > >
> > > On Thu, 30 Jan 2025 at 00:21, Ilias Apalodimas
> > > <ilias.apalodimas at linaro.org> wrote:
> > > >
> > > > U-Boot maps all pages as RWX. Sadly it's not not 1990 anymore and we are
> > > > better off mapping binaries with proper permissions.
> > > >
> > > > This is an attempt to map the U-Boot binary properly, but leave the
> > > > area we load binaries unaffected and RWX.
> > > >
> > > > patch #1 adds printing capabilities for page permissions in meminfo
> > > > patch #2 prepares our linker scripts, aligns sections in page boundaries etc
> > > > patch #3 is adding a function to change page tables
> > > > patch #4 sets the permissions for .rodata, .text and .data
> > > >
> > > > There's a few problems problem in this RFC ...
> > > > - U-Boot has no MMU APIs in place. As a result I just wired up the function
> > > > changing the page permissions in board_r.c but only for arm64. In the long
> > > > term we should add an API that other archs can use if they wish/can
> > >
> > > But this creates more work for others. It would be better to do the
> > > job properly at the start. You don't need to support other archs, but
> > > you should create a plausible API and some structs which others can
> > > use. See cpu.h for some ideas. Of course you can't predict the future,
> > > but others will build on it if you make an effort. Otherwise, I doubt
> > > anyone else will (later) clean it up.
> >
> > I can move that function to cpu_ops.h and have if NULL for other archs
> >
> > >
> > > > - meminfo doesn't align all results properly (Caleb?)
> > > > - I am not setting the permissions of EFI runtime services section on purpose.
> > > > Since the OS is allowed to call SetVirtualAddressMap, we need to reset the
> > > > pages to RWX just before ExitBootServices, so the OS can relocate that code.
> > > > In arm64 this isn't a huge problem, because we explicitly disable SVAM if
> > > > if VA_BITS > 39, but other OSes/archs will have a problem.
> > > >
> > > > # TODO:
> > > > - Long term. Add an MMU API and use that instead of exporting arch specific
> > > > functions
> > > > - Add an enum in mmu_set_attrs() instead of 1,2,3 arguments
> > > > - Set the permissions of EFI runtime services anbd reset them before EBS()
> > > > - Fix alignment when printing pages & information
> > > > - Add a Kconfig option so the feature can be turned off.
> > > > The reason is that QEMU CI and some boards, fail because they are trying to
> > > > write RO pages. This usually happens due to variables being wrongly defined as
> > > > const, but with the updated page permissions this leads to a crash [0] [1].
> > > > In both cases the reported ESR is 0x9600004f which translates to
> > > > "Abort caused by writing to memory" "Permission fault, level 3.". On top of
> > > > that not setting pages as RO (and only setting .data and .text sections) works
> > > > fine. So until we find and fix the bugs above we can't turn this on
> > > > unconditionally.
> > > >
> > > > # Open questions
> > > > - Is initr_reloc_global_data() the right place to change permissions? Or is there
> > > > a better/safer place to do that?
> > > >
> > > > # How to test patches
> > > > - Aplly them an enable
> > > > CONFIG_CMD_MEMINFO=y
> > > > CONFIG_CMD_MEMINFO_MAP=y
> > > > 'meminfo' should print something along the lines of
> > > > => meminfo
> > > > DRAM: 8 GiB
> > > > Walking pagetable at 000000023ffe0000, va_bits: 40. Using 4 levels
> > > > [0x23ffe1000] | Table | |
> > > > [0x23ffe2000] | Table | |
> > > > [0x000000000 - 0x008000000] | Block | RWX | Normal | Inner-shareable
> > > > [0x008000000 - 0x040000000] | Block | RW | Device-nGnRnE | Non-shareable
> > > > [0x040000000 - 0x200000000] | Block | RWX | Normal | Inner-shareable
> > > > [0x23ffea000] | Table | |
> > > > [0x200000000 - 0x23f600000] | Block | RWX | Normal | Inner-shareable
> > > > [0x23ffeb000] | Table | |
> > > > [0x23f600000 - 0x23f68b000] | Pages | RWX | Normal | Inner-shareable
> > > > [0x23f68b000 - 0x23f74e000] | Pages | RX | Normal | Inner-shareable
> > > > [0x23f74e000 - 0x23f793000] | Pages | RO | Normal | Inner-shareable
> > > > [0x23f793000 - 0x23f794000] | Pages | RWX | Normal | Inner-shareable
> > > > [0x23f794000 - 0x23f79d000] | Pages | RW | Normal | Inner-shareable
> > > > [0x23f79d000 - 0x23f800000] | Pages | RWX | Normal | Inner-shareable
> > > > [0x23f800000 - 0x240000000] | Block | RWX | Normal | Inner-shareable
> > > > [0x240000000 - 0x4000000000] | Block | RWX | Normal | Inner-shareable
> > > > [0x23ffe3000] | Table | |
> > > > [0x4010000000 - 0x4020000000] | Block | RW | Device-nGnRnE | Non-shareable
> > > > [0x23ffe4000] | Table | |
> > > > [0x8000000000 - 0x10000000000] | Block | RW | Device-nGnRnE | Non-shareable
> > >
> > > No, this is not a memory map.
> >
> > This is *literally* the memory map.
>
> The memory map currently has a single address and describes what each
> region is for. This looks like a detailed list of some other
> attributes.
>
> >
> > > Please make all that stuff an option.
> > > Try to use generic structs to print it, not ARM-specific code.
> >
> > How? The information in the page tables is arch specific.
>
> enum cpu_mem_permission {
> CPUMP_RO = BIT(0),
> CPUMP_RW = BIT(1),
> etc.
> };
We have that to set the options.
The RFC was also printing a generic RW, RX, RO, but people wanted to
be able to print arch-specific flags when dumping it.
>
> struct cpu_mem_attrs {
> uint permission; /* enum cpu_mem_permission */
> (more things here)
> };
>
> Regards,
> Simon
>
>
/Ilias
> >
> > Thanks
> > /Ilias
> > >
> > > >
> > > > [0] https://lore.kernel.org/u-boot/20250129-rockchip-pinctrl-const-v1-0-450ccdadfa7e@cherry.de/
> > > > [1] https://source.denx.de/u-boot/custodians/u-boot-tpm/-/jobs/1008714
> > > >
> > > > Ilias Apalodimas (4):
> > > > meminfo: add memory details for armv8
> > > > arm: Prepare linker scripts for memory permissions
> > > > arm64: mmu_change_region_attr() add an option not to break PTEs
> > > > arm64: Change mapping for data/rodata/text
> > > >
> > > > Makefile | 15 +++++----
> > > > arch/arm/cpu/armv8/cache_v8.c | 45 +++++++++++++++++++++++--
> > > > arch/arm/cpu/armv8/fsl-layerscape/cpu.c | 10 +++---
> > > > arch/arm/cpu/armv8/u-boot.lds | 32 +++++++++++-------
> > > > arch/arm/include/asm/armv8/mmu.h | 2 ++
> > > > arch/arm/include/asm/system.h | 3 +-
> > > > arch/arm/mach-snapdragon/board.c | 2 +-
> > > > cmd/meminfo.c | 5 +++
> > > > common/board_r.c | 7 ++++
> > > > include/asm-generic/sections.h | 2 ++
> > > > lib/efi_loader/efi_runtime.c | 2 ++
> > > > 11 files changed, 97 insertions(+), 28 deletions(-)
> > > >
> > > > --
> > > > 2.43.0
> > > >
> > >
> > > Regards,
> > > Simon
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