Re: [PATCH v4] x86, efi: never relocate kernel below lowest acceptable address

From: Ard Biesheuvel
Date: Tue Oct 22 2019 - 02:14:10 EST

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On Thu, 17 Oct 2019 at 11:30, Kairui Song <kasong@xxxxxxxxxx> wrote:
>
> Currently, kernel fails to boot on some HyperV VMs when using EFI.
> And it's a potential issue on all platforms.
>
> It's caused by broken kernel relocation on EFI systems, when below three
> conditions are met:
>
> 1. Kernel image is not loaded to the default address (LOAD_PHYSICAL_ADDR)
> by the loader.
> 2. There isn't enough room to contain the kernel, starting from the
> default load address (eg. something else occupied part the region).
> 3. In the memmap provided by EFI firmware, there is a memory region
> starts below LOAD_PHYSICAL_ADDR, and suitable for containing the
> kernel.
>
> EFI stub will perform a kernel relocation when condition 1 is met. But
> due to condition 2, EFI stub can't relocate kernel to the preferred
> address, so it fallback to ask EFI firmware to alloc lowest usable memory
> region, got the low region mentioned in condition 3, and relocated
> kernel there.
>
> It's incorrect to relocate the kernel below LOAD_PHYSICAL_ADDR. This
> is the lowest acceptable kernel relocation address.
>
> The first thing goes wrong is in arch/x86/boot/compressed/head_64.S.
> Kernel decompression will force use LOAD_PHYSICAL_ADDR as the output
> address if kernel is located below it. Then the relocation before
> decompression, which move kernel to the end of the decompression buffer,
> will overwrite other memory region, as there is no enough memory there.
>
> To fix it, just don't let EFI stub relocate the kernel to any address
> lower than lowest acceptable address.
>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxx>
> Acked-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
>

Ingo, Boris, could you please comment on this?

Apologies for not responding with review comments until now, but I was
waiting for someone from team-x86 to acknowledge the issue and confirm
a fix is needed.

Some comments below.

> ---
> Update from V3:
> - Update commit message.
>
> Update from V2:
> - Update part of the commit message.
>
> Update from V1:
> - Redo the commit message.
>
> arch/x86/boot/compressed/eboot.c | 8 +++++---
> drivers/firmware/efi/libstub/arm32-stub.c | 2 +-
> drivers/firmware/efi/libstub/arm64-stub.c | 2 +-
> drivers/firmware/efi/libstub/efi-stub-helper.c | 12 ++++++++----
> include/linux/efi.h | 5 +++--
> 5 files changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
> index d6662fdef300..e89e84b66527 100644
> --- a/arch/x86/boot/compressed/eboot.c
> +++ b/arch/x86/boot/compressed/eboot.c
> @@ -13,6 +13,7 @@
> #include <asm/e820/types.h>
> #include <asm/setup.h>
> #include <asm/desc.h>
> +#include <asm/boot.h>
>
> #include "../string.h"
> #include "eboot.h"
> @@ -413,7 +414,7 @@ struct boot_params *make_boot_params(struct efi_config *c)
> }
>
> status = efi_low_alloc(sys_table, 0x4000, 1,
> - (unsigned long *)&boot_params);
> + (unsigned long *)&boot_params, 0);

Instead of changing the calls to efi_low_alloc() everywhere, could you
please only update the implementation to take a 'min' argument, and
rename it to something like ' ()', Then, the original extern
declaration of efi_low_alloc() can be converted into a static inline
that calls efi_low_alloc_above. That also allows us to pull the 'alloc
at 0x0' logic out of the loop, e.g.,

efi_status_t efi_low_alloc_above(efi_system_table_t *sys_table_arg,
unsigned long size, unsigned long align,
unsigned long *addr, unsigned long min);

static inline
efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg,
unsigned long size, unsigned long align,
unsigned long *addr)
{
/*
* Don't allocate at 0x0. It will confuse code that
* checks pointers against NULL. Skip the first 8
* bytes so we start at a nice even number.
*/
return efi_low_alloc_above(sys_table_arg, size, align, addr, 8);
}

(and drop the same logic from the function implementation)

> if (status != EFI_SUCCESS) {
> efi_printk(sys_table, "Failed to allocate lowmem for boot params\n");
> return NULL;
> @@ -798,7 +799,7 @@ efi_main(struct efi_config *c, struct boot_params *boot_params)
>
> gdt->size = 0x800;
> status = efi_low_alloc(sys_table, gdt->size, 8,
> - (unsigned long *)&gdt->address);
> + (unsigned long *)&gdt->address, 0);
> if (status != EFI_SUCCESS) {
> efi_printk(sys_table, "Failed to allocate memory for 'gdt'\n");
> goto fail;
> @@ -813,7 +814,8 @@ efi_main(struct efi_config *c, struct boot_params *boot_params)
> status = efi_relocate_kernel(sys_table, &bzimage_addr,
> hdr->init_size, hdr->init_size,
> hdr->pref_address,
> - hdr->kernel_alignment);
> + hdr->kernel_alignment,
> + LOAD_PHYSICAL_ADDR);
> if (status != EFI_SUCCESS) {
> efi_printk(sys_table, "efi_relocate_kernel() failed!\n");
> goto fail;
> diff --git a/drivers/firmware/efi/libstub/arm32-stub.c b/drivers/firmware/efi/libstub/arm32-stub.c
> index e8f7aefb6813..bf6f954d6afe 100644
> --- a/drivers/firmware/efi/libstub/arm32-stub.c
> +++ b/drivers/firmware/efi/libstub/arm32-stub.c
> @@ -220,7 +220,7 @@ efi_status_t handle_kernel_image(efi_system_table_t *sys_table,
> *image_size = image->image_size;
> status = efi_relocate_kernel(sys_table, image_addr, *image_size,
> *image_size,
> - dram_base + MAX_UNCOMP_KERNEL_SIZE, 0);
> + dram_base + MAX_UNCOMP_KERNEL_SIZE, 0, 0);
> if (status != EFI_SUCCESS) {
> pr_efi_err(sys_table, "Failed to relocate kernel.\n");
> efi_free(sys_table, *reserve_size, *reserve_addr);
> diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
> index 1550d244e996..3d2e517e10f4 100644
> --- a/drivers/firmware/efi/libstub/arm64-stub.c
> +++ b/drivers/firmware/efi/libstub/arm64-stub.c
> @@ -140,7 +140,7 @@ efi_status_t handle_kernel_image(efi_system_table_t *sys_table_arg,
> if (status != EFI_SUCCESS) {
> *reserve_size = kernel_memsize + TEXT_OFFSET;
> status = efi_low_alloc(sys_table_arg, *reserve_size,
> - MIN_KIMG_ALIGN, reserve_addr);
> + MIN_KIMG_ALIGN, reserve_addr, 0);
>
> if (status != EFI_SUCCESS) {
> pr_efi_err(sys_table_arg, "Failed to relocate kernel\n");
> diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
> index 3caae7f2cf56..00b00a2562aa 100644
> --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
> +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
> @@ -260,11 +260,11 @@ efi_status_t efi_high_alloc(efi_system_table_t *sys_table_arg,
> }
>
> /*
> - * Allocate at the lowest possible address.
> + * Allocate at the lowest possible address that is not below 'min'.
> */
> efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg,
> unsigned long size, unsigned long align,
> - unsigned long *addr)
> + unsigned long *addr, unsigned long min)
> {
> unsigned long map_size, desc_size, buff_size;
> efi_memory_desc_t *map;
> @@ -311,6 +311,9 @@ efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg,
> start = desc->phys_addr;
> end = start + desc->num_pages * EFI_PAGE_SIZE;
>
> + if (start < min)
> + start = min;
> +
> /*
> * Don't allocate at 0x0. It will confuse code that
> * checks pointers against NULL. Skip the first 8
> @@ -698,7 +701,8 @@ efi_status_t efi_relocate_kernel(efi_system_table_t *sys_table_arg,
> unsigned long image_size,
> unsigned long alloc_size,
> unsigned long preferred_addr,
> - unsigned long alignment)
> + unsigned long alignment,
> + unsigned long min_addr)
> {
> unsigned long cur_image_addr;
> unsigned long new_addr = 0;
> @@ -732,7 +736,7 @@ efi_status_t efi_relocate_kernel(efi_system_table_t *sys_table_arg,
> */
> if (status != EFI_SUCCESS) {
> status = efi_low_alloc(sys_table_arg, alloc_size, alignment,
> - &new_addr);
> + &new_addr, min_addr);
> }
> if (status != EFI_SUCCESS) {
> pr_efi_err(sys_table_arg, "Failed to allocate usable memory for kernel.\n");
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index bd3837022307..a5144cc44e54 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -1581,7 +1581,7 @@ efi_status_t efi_get_memory_map(efi_system_table_t *sys_table_arg,
>
> efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg,
> unsigned long size, unsigned long align,
> - unsigned long *addr);
> + unsigned long *addr, unsigned long min);
>
> efi_status_t efi_high_alloc(efi_system_table_t *sys_table_arg,
> unsigned long size, unsigned long align,
> @@ -1592,7 +1592,8 @@ efi_status_t efi_relocate_kernel(efi_system_table_t *sys_table_arg,
> unsigned long image_size,
> unsigned long alloc_size,
> unsigned long preferred_addr,
> - unsigned long alignment);
> + unsigned long alignment,
> + unsigned long min_addr);
>
> efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg,
> efi_loaded_image_t *image,
> --
> 2.21.0
>

Next message: Rajendra Nayak: "Re: [PATCH v2 02/13] arm64: dts: sc7180: Add minimal dts/dtsi files for SC7180 soc"
Previous message: Herbert Xu: "Re: [PATCH] xfrm : lock input tasklet skb queue"
In reply to: Kairui Song: "[PATCH v4] x86, efi: never relocate kernel below lowest acceptable address"
Next in thread: Borislav Petkov: "Re: [PATCH v4] x86, efi: never relocate kernel below lowest acceptable address"
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