From: Julien Grall Date: Wed, 15 May 2019 20:17:30 +0000 (+0100) Subject: xen/arm: traps: Avoid using BUG_ON() to check guest state in advance_pc() X-Git-Tag: archive/raspbian/4.11.3+24-g14b62ab3e5-1+rpi1^2~55^2~74 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=7f5f48dff399cb4739dc74f136fa605a0eaad1d5;p=xen.git xen/arm: traps: Avoid using BUG_ON() to check guest state in advance_pc() The condition of the BUG_ON() in advance_pc() is pretty wrong because the bits [26:25] and [15:10] have a different meaning between AArch32 and AArch64 state. On AArch32, they are used to store PSTATE.IT. On AArch64, they are RES0 or used for new feature (e.g ARMv8.0-SSBS, ARMv8.5-BTI). This means a 64-bit guest will hit the BUG_ON() if it is trying to use any of these features. More generally, RES0 means that the bits is reserved for future use. So crashing the host is definitely not the right solution. In this particular case, we only need to know the guest was using 32-bit Mode and the Thumb instructions. So replace the BUG_ON() by a proper check. Reported-by: Lukas Jünger Signed-off-by: Julien Grall Reviewed-by: Stefano Stabellini (cherry picked from commit 72615f2e6b98e861c08abb1d2b194126013d54fe) --- diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c index 2a32441a61..e930585ad6 100644 --- a/xen/arch/arm/traps.c +++ b/xen/arch/arm/traps.c @@ -1654,12 +1654,9 @@ int check_conditional_instr(struct cpu_user_regs *regs, const union hsr hsr) void advance_pc(struct cpu_user_regs *regs, const union hsr hsr) { unsigned long itbits, cond, cpsr = regs->cpsr; + bool is_thumb = psr_mode_is_32bit(cpsr) && (cpsr & PSR_THUMB); - /* PSR_IT_MASK bits can only be set for 32-bit processors in Thumb mode. */ - BUG_ON( (!psr_mode_is_32bit(cpsr)||!(cpsr&PSR_THUMB)) - && (cpsr&PSR_IT_MASK) ); - - if ( cpsr&PSR_IT_MASK ) + if ( is_thumb && (cpsr & PSR_IT_MASK) ) { /* The ITSTATE[7:0] block is contained in CPSR[15:10],CPSR[26:25] *