* [PATCH] arm64: warn on incorrect placement of the kernel by the bootloader
@ 2020-06-10 17:46 Ard Biesheuvel
2020-06-11 11:51 ` Will Deacon
0 siblings, 1 reply; 3+ messages in thread
From: Ard Biesheuvel @ 2020-06-10 17:46 UTC (permalink / raw)
To: linux-arm-kernel; +Cc: mark.rutland, maz, will, Ard Biesheuvel, jonathan
Commit cfa7ede20f133c ("arm64: set TEXT_OFFSET to 0x0 in preparation for
removing it entirely") results in boot failures when booting kernels that
are built without KASLR support on broken bootloaders that ignore the
TEXT_OFFSET value passed via the header, and use the default of 0x80000
instead.
To work around this, turn CONFIG_RELOCATABLE on by default, even if KASLR
itself (CONFIG_RANDOMIZE_BASE) is turned off, and require CONFIG_EXPERT
to be enabled to deviate from this. Then, emit a warning into the kernel
log if we are not booting via the EFI stub (which is permitted to deviate
from the placement restrictions) and the kernel base address is not placed
according to the rules as laid out in Documentation/arm64/booting.rst.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/Kconfig | 3 ++-
arch/arm64/kernel/setup.c | 3 +++
2 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7f9d38444d6d..16c3f158c80e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1740,8 +1740,9 @@ config ARM64_DEBUG_PRIORITY_MASKING
endif
config RELOCATABLE
- bool
+ bool "Build a relocatable kernel image" if EXPERT
select ARCH_HAS_RELR
+ default y
help
This builds the kernel as a Position Independent Executable (PIE),
which retains all relocation metadata required to relocate the
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 3fd2c11c09fc..bfeeeea833dd 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -319,6 +319,9 @@ void __init setup_arch(char **cmdline_p)
xen_early_init();
efi_init();
+ WARN(!efi_enabled(EFI_BOOT) && ((u64)_text % MIN_KIMG_ALIGN) != 0,
+ FW_BUG "Kernel image misaligned at boot, please fix your bootloader");
+
arm64_memblock_init();
paging_init();
--
2.26.2
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^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] arm64: warn on incorrect placement of the kernel by the bootloader
2020-06-10 17:46 [PATCH] arm64: warn on incorrect placement of the kernel by the bootloader Ard Biesheuvel
@ 2020-06-11 11:51 ` Will Deacon
2020-06-11 11:53 ` Ard Biesheuvel
0 siblings, 1 reply; 3+ messages in thread
From: Will Deacon @ 2020-06-11 11:51 UTC (permalink / raw)
To: Ard Biesheuvel; +Cc: mark.rutland, maz, jonathan, linux-arm-kernel
On Wed, Jun 10, 2020 at 07:46:01PM +0200, Ard Biesheuvel wrote:
> Commit cfa7ede20f133c ("arm64: set TEXT_OFFSET to 0x0 in preparation for
> removing it entirely") results in boot failures when booting kernels that
> are built without KASLR support on broken bootloaders that ignore the
> TEXT_OFFSET value passed via the header, and use the default of 0x80000
> instead.
>
> To work around this, turn CONFIG_RELOCATABLE on by default, even if KASLR
> itself (CONFIG_RANDOMIZE_BASE) is turned off, and require CONFIG_EXPERT
> to be enabled to deviate from this. Then, emit a warning into the kernel
> log if we are not booting via the EFI stub (which is permitted to deviate
> from the placement restrictions) and the kernel base address is not placed
> according to the rules as laid out in Documentation/arm64/booting.rst.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> arch/arm64/Kconfig | 3 ++-
> arch/arm64/kernel/setup.c | 3 +++
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7f9d38444d6d..16c3f158c80e 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1740,8 +1740,9 @@ config ARM64_DEBUG_PRIORITY_MASKING
> endif
>
> config RELOCATABLE
> - bool
> + bool "Build a relocatable kernel image" if EXPERT
> select ARCH_HAS_RELR
> + default y
> help
> This builds the kernel as a Position Independent Executable (PIE),
> which retains all relocation metadata required to relocate the
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 3fd2c11c09fc..bfeeeea833dd 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -319,6 +319,9 @@ void __init setup_arch(char **cmdline_p)
>
> xen_early_init();
> efi_init();
> + WARN(!efi_enabled(EFI_BOOT) && ((u64)_text % MIN_KIMG_ALIGN) != 0,
> + FW_BUG "Kernel image misaligned at boot, please fix your bootloader");
I think pr_warn is probably sufficient here, as the backtrace isn't really
helping anybody:
[ 0.000000] ------------[ cut here ]------------
[ 0.000000] [Firmware Bug]: Kernel image misaligned at boot, please fix your bootloader
[ 0.000000] WARNING: CPU: 0 PID: 0 at arch/arm64/kernel/setup.c:323 setup_arch+0x208/0x214
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.7.0-rc3-00162-g16d1072f6b69 #1
[ 0.000000] Hardware name: linux,dummy-virt (DT)
[ 0.000000] pstate: 60000085 (nZCv daIf -PAN -UAO BTYPE=--)
[ 0.000000] pc : setup_arch+0x208/0x214
[ 0.000000] lr : setup_arch+0x208/0x214
[ 0.000000] sp : ffff800011b03f90
[ 0.000000] x29: ffff800011b03f90 x28: 0000000081580018
[ 0.000000] x27: 0000000000000000 x26: 0000000000000000
[ 0.000000] x25: 0000000000000000 x24: 0000000000000000
[ 0.000000] x23: 0000000000080000 x22: 0000000000000000
[ 0.000000] x21: 000000008fe00000 x20: ffff800011b09000
[ 0.000000] x19: ffff800010080000 x18: 000000000001fdd8
[ 0.000000] x17: 000000000000004a x16: ffff800011b03bf1
[ 0.000000] x15: 0000000000000000 x14: 6564616f6c746f6f
[ 0.000000] x13: 0000000000000000 x12: 0000000000000000
[ 0.000000] x11: 0000000000000000 x10: 00000000ffffffff
[ 0.000000] x9 : 0000000000000000 x8 : 0000000000000000
[ 0.000000] x7 : 000000000000004b x6 : ffff800011d41093
[ 0.000000] x5 : 000000000000004b x4 : 000000000000000c
[ 0.000000] x3 : 0000000000000072 x2 : 000000000000003f
[ 0.000000] x1 : ffff800011d3e75f x0 : 000000000000004b
[ 0.000000] Call trace:
[ 0.000000] setup_arch+0x208/0x214
[ 0.000000] start_kernel+0x70/0x3ec
[ 0.000000] random: get_random_bytes called from __warn+0xe4/0x178 with crng_init=0
[ 0.000000] ---[ end trace 0000000000000000 ]---
Will
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] arm64: warn on incorrect placement of the kernel by the bootloader
2020-06-11 11:51 ` Will Deacon
@ 2020-06-11 11:53 ` Ard Biesheuvel
0 siblings, 0 replies; 3+ messages in thread
From: Ard Biesheuvel @ 2020-06-11 11:53 UTC (permalink / raw)
To: Will Deacon; +Cc: Mark Rutland, Marc Zyngier, Jonathan Marek, Linux ARM
On Thu, 11 Jun 2020 at 13:51, Will Deacon <will@kernel.org> wrote:
>
> On Wed, Jun 10, 2020 at 07:46:01PM +0200, Ard Biesheuvel wrote:
> > Commit cfa7ede20f133c ("arm64: set TEXT_OFFSET to 0x0 in preparation for
> > removing it entirely") results in boot failures when booting kernels that
> > are built without KASLR support on broken bootloaders that ignore the
> > TEXT_OFFSET value passed via the header, and use the default of 0x80000
> > instead.
> >
> > To work around this, turn CONFIG_RELOCATABLE on by default, even if KASLR
> > itself (CONFIG_RANDOMIZE_BASE) is turned off, and require CONFIG_EXPERT
> > to be enabled to deviate from this. Then, emit a warning into the kernel
> > log if we are not booting via the EFI stub (which is permitted to deviate
> > from the placement restrictions) and the kernel base address is not placed
> > according to the rules as laid out in Documentation/arm64/booting.rst.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> > arch/arm64/Kconfig | 3 ++-
> > arch/arm64/kernel/setup.c | 3 +++
> > 2 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 7f9d38444d6d..16c3f158c80e 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -1740,8 +1740,9 @@ config ARM64_DEBUG_PRIORITY_MASKING
> > endif
> >
> > config RELOCATABLE
> > - bool
> > + bool "Build a relocatable kernel image" if EXPERT
> > select ARCH_HAS_RELR
> > + default y
> > help
> > This builds the kernel as a Position Independent Executable (PIE),
> > which retains all relocation metadata required to relocate the
> > diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> > index 3fd2c11c09fc..bfeeeea833dd 100644
> > --- a/arch/arm64/kernel/setup.c
> > +++ b/arch/arm64/kernel/setup.c
> > @@ -319,6 +319,9 @@ void __init setup_arch(char **cmdline_p)
> >
> > xen_early_init();
> > efi_init();
> > + WARN(!efi_enabled(EFI_BOOT) && ((u64)_text % MIN_KIMG_ALIGN) != 0,
> > + FW_BUG "Kernel image misaligned at boot, please fix your bootloader");
>
> I think pr_warn is probably sufficient here, as the backtrace isn't really
> helping anybody:
>
It makes it a bit more obnoxious, and so people are more likely to
notice and care. But I agree that the backtrace serves no purpose.
I'll update that.
> [ 0.000000] ------------[ cut here ]------------
> [ 0.000000] [Firmware Bug]: Kernel image misaligned at boot, please fix your bootloader
> [ 0.000000] WARNING: CPU: 0 PID: 0 at arch/arm64/kernel/setup.c:323 setup_arch+0x208/0x214
> [ 0.000000] Modules linked in:
> [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.7.0-rc3-00162-g16d1072f6b69 #1
> [ 0.000000] Hardware name: linux,dummy-virt (DT)
> [ 0.000000] pstate: 60000085 (nZCv daIf -PAN -UAO BTYPE=--)
> [ 0.000000] pc : setup_arch+0x208/0x214
> [ 0.000000] lr : setup_arch+0x208/0x214
> [ 0.000000] sp : ffff800011b03f90
> [ 0.000000] x29: ffff800011b03f90 x28: 0000000081580018
> [ 0.000000] x27: 0000000000000000 x26: 0000000000000000
> [ 0.000000] x25: 0000000000000000 x24: 0000000000000000
> [ 0.000000] x23: 0000000000080000 x22: 0000000000000000
> [ 0.000000] x21: 000000008fe00000 x20: ffff800011b09000
> [ 0.000000] x19: ffff800010080000 x18: 000000000001fdd8
> [ 0.000000] x17: 000000000000004a x16: ffff800011b03bf1
> [ 0.000000] x15: 0000000000000000 x14: 6564616f6c746f6f
> [ 0.000000] x13: 0000000000000000 x12: 0000000000000000
> [ 0.000000] x11: 0000000000000000 x10: 00000000ffffffff
> [ 0.000000] x9 : 0000000000000000 x8 : 0000000000000000
> [ 0.000000] x7 : 000000000000004b x6 : ffff800011d41093
> [ 0.000000] x5 : 000000000000004b x4 : 000000000000000c
> [ 0.000000] x3 : 0000000000000072 x2 : 000000000000003f
> [ 0.000000] x1 : ffff800011d3e75f x0 : 000000000000004b
> [ 0.000000] Call trace:
> [ 0.000000] setup_arch+0x208/0x214
> [ 0.000000] start_kernel+0x70/0x3ec
> [ 0.000000] random: get_random_bytes called from __warn+0xe4/0x178 with crng_init=0
> [ 0.000000] ---[ end trace 0000000000000000 ]---
>
> Will
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-06-10 17:46 [PATCH] arm64: warn on incorrect placement of the kernel by the bootloader Ard Biesheuvel
2020-06-11 11:51 ` Will Deacon
2020-06-11 11:53 ` Ard Biesheuvel
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