On Tue, May 31, 2022 at 10:29:14AM +0200, Ahmad Fatoum wrote:
> arm_cpu_lowlevel_init() is usually called first thing and will ensure
> barebox runs in SVC mode. If barebox is started in HYP mode instead,
> like is the case on Raspberry Pi 2-3, it will do an exception return
> into SVC mode, which will bank the previously used SP_Hyp and
> restore SP_Svc that may not have been properly initialized by barebox.
>
> This wasn't too bad so far, because arm_setup_stack was usually called
> after arm_cpu_lowlevel_init, but with ENTRY_FUNCTION_WITHSTACK, SP is
> initialized early on in the naked entry point with
> arm_cpu_lowlevel_init() being called after that.
>
> This can lead to spurious boot hangs in the Raspberry Pi 2 and 3 entry
> points. Fix this by always saving sp to r3 and restoring it, like we do
> with lr. This is safe to do, because r3 isn't clobbered by any
> instruction in arm_cpu_lowlevel_init() and because it's an argument
> register, callers have to expect it being overwritten by the callee.
>
> Fixes: b267578d0567 ("ARM: rpi: use ENTRY_FUNCTION_WITHSTACK to prepare for ARM64 support")
> Fixes: 41292192c01b ("ARM: safely switch from HYP to SVC mode if required")
> Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
> ---
> v1 -> v2:
> - add source code comment on why sp is saved (Sascha)
> ---
> arch/arm/cpu/lowlevel.S | 3 +++
> 1 file changed, 3 insertions(+)
Applied, thanks
Sascha
>
> diff --git a/arch/arm/cpu/lowlevel.S b/arch/arm/cpu/lowlevel.S
> index 5a7dd3c2093f..960a92b78c0a 100644
> --- a/arch/arm/cpu/lowlevel.S
> +++ b/arch/arm/cpu/lowlevel.S
> @@ -9,6 +9,8 @@
> ENTRY(arm_cpu_lowlevel_init)
> /* save lr, since it may be banked away with a processor mode change */
> mov r2, lr
> + /* save sp, because possible HYP -> SVC transition below clobbers it */
> + mov r3, sp
>
> #ifdef CONFIG_CPU_32v7
> /* careful: the hyp install corrupts r0 and r1 */
> @@ -77,6 +79,7 @@ THUMB( orr r12, r12, #PSR_T_BIT )
>
> mcr p15, 0, r12, c1, c0, 0 /* SCTLR */
>
> + mov sp, r3
> mov pc, r2
> ENDPROC(arm_cpu_lowlevel_init)
>
> --
> 2.30.2
>
>
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>
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