Re: [PATCH 2/2] arm64: don't load 32-bit binaries if platform has no aarch32_el0

[Yury]

On Tue, Sep 01, 2015 at 05:04:26PM +0100, Mark Rutland wrote:
> On Tue, Sep 01, 2015 at 03:41:12PM +0100, Yury Norov wrote:
> > Kernel option COMPAT defines the ability of executing aarch32 binaries.
> > Some platforms does not support aarch32 mode, and so cannot execute that
> > binaries. But we cannot just disable COMPAT for them because the same
> > kernel binary may be used by multiple platforms.
> > 
> > In this patch, system_supports_aarch32_el0() is introduced to detect
> > aarch32 support at run-time.
> > 
> > Signed-off-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
> > ---
> >  arch/arm64/include/asm/cpufeature.h | 1 +
> >  arch/arm64/include/asm/elf.h        | 6 ++++--
> >  arch/arm64/kernel/cpuinfo.c         | 9 +++++++++
> >  3 files changed, 14 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> > index 20cdc26..d24ea15 100644
> > --- a/arch/arm64/include/asm/cpufeature.h
> > +++ b/arch/arm64/include/asm/cpufeature.h
> > @@ -81,6 +81,7 @@ void check_local_cpu_errata(void);
> >  void check_local_cpu_features(void);
> >  bool cpu_supports_mixed_endian_el0(void);
> >  bool system_supports_mixed_endian_el0(void);
> > +bool system_supports_aarch32_el0(void);
> >  
> >  #endif /* __ASSEMBLY__ */
> >  
> > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> > index faad6df..461897b 100644
> > --- a/arch/arm64/include/asm/elf.h
> > +++ b/arch/arm64/include/asm/elf.h
> > @@ -21,6 +21,7 @@
> >  /*
> >   * ELF register definitions..
> >   */
> > +#include <asm/cpufeature.h>
> >  #include <asm/ptrace.h>
> >  #include <asm/user.h>
> >  
> > @@ -173,8 +174,9 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
> >  
> >  /* AArch32 EABI. */
> >  #define EF_ARM_EABI_MASK		0xff000000
> > -#define compat_elf_check_arch(x)	(((x)->e_machine == EM_ARM) && \
> > -					 ((x)->e_flags & EF_ARM_EABI_MASK))
> > +#define compat_elf_check_arch(x)	(system_supports_aarch32_el0()	\
> > +					&& ((x)->e_machine == EM_ARM)	\
> > +					&& ((x)->e_flags & EF_ARM_EABI_MASK))
> >  
> >  #define compat_start_thread		compat_start_thread
> >  #define COMPAT_SET_PERSONALITY(ex)	set_thread_flag(TIF_32BIT);
> > diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> > index 75d5a86..95d953f 100644
> > --- a/arch/arm64/kernel/cpuinfo.c
> > +++ b/arch/arm64/kernel/cpuinfo.c
> > @@ -79,6 +79,15 @@ bool system_supports_mixed_endian_el0(void)
> >  	return mixed_endian_el0;
> >  }
> >  
> > +#define AARCH64		1
> > +#define AARCH32_64	2
> 
> These should be better namespaced. Perhaps ID_AA64PFR0_EL1_EL0_64 and
> ID_AA64PFR0_EL1_EL0_6432 ?
> 
> > +bool system_supports_aarch32_el0(void)
> > +{
> > +	struct cpuinfo_arm64 *info = this_cpu_ptr(&cpu_data);
> > +	u64 arm64_el0 = info->reg_id_aa64pfr0 & 0xf;
> > +	return arm64_el0 == AARCH32_64;
> > +}
> 
> We should handle this the same way as we do for endianness support and
> check that all CPUs support AArch32, and set a global flag, rather than
> assuming that all CPUs are symmetric. Likewise for any other feature we
> have to dynamically detect.
> 

OK. Will do in V2

> Thanks,
> Mark.
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