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    SubjectRe: [PATCH] arm64: add check_wx_pages debugfs for CHECK_WX
    On Mon, Mar 09, 2020 at 12:17:14PM +0000, Mark Rutland wrote:
    > On Sat, Mar 07, 2020 at 04:39:26PM +0700, Phong Tran wrote:
    > > follow the suggestion from
    > > https://github.com/KSPP/linux/issues/35
    >
    > That says:
    >
    > | This should be implemented for all architectures
    >
    > ... so surely this should be in generic code, rahter than being
    > arm64-specific?
    >
    > Thanks,
    > Mark.
    >
    > >
    > > Signed-off-by: Phong Tran <tranmanphong@gmail.com>
    > > ---
    > > arch/arm64/Kconfig.debug | 3 ++-
    > > arch/arm64/include/asm/ptdump.h | 2 ++
    > > arch/arm64/mm/dump.c | 1 +
    > > arch/arm64/mm/ptdump_debugfs.c | 18 ++++++++++++++++++
    > > 4 files changed, 23 insertions(+), 1 deletion(-)
    > >
    > > diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
    > > index 1c906d932d6b..be552fa351e2 100644
    > > --- a/arch/arm64/Kconfig.debug
    > > +++ b/arch/arm64/Kconfig.debug
    > > @@ -48,7 +48,8 @@ config DEBUG_WX
    > > of other unfixed kernel bugs easier.
    > >
    > > There is no runtime or memory usage effect of this option
    > > - once the kernel has booted up - it's a one time check.
    > > + once the kernel has booted up - it's a one time check and
    > > + can be checked by echo "1" to "check_wx_pages" debugfs in runtime.
    > >
    > > If in doubt, say "Y".
    > >
    > > diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
    > > index 38187f74e089..b80d6b4fc508 100644
    > > --- a/arch/arm64/include/asm/ptdump.h
    > > +++ b/arch/arm64/include/asm/ptdump.h
    > > @@ -24,9 +24,11 @@ struct ptdump_info {
    > > void ptdump_walk(struct seq_file *s, struct ptdump_info *info);
    > > #ifdef CONFIG_PTDUMP_DEBUGFS
    > > void ptdump_debugfs_register(struct ptdump_info *info, const char *name);
    > > +int ptdump_check_wx_init(void);
    > > #else
    > > static inline void ptdump_debugfs_register(struct ptdump_info *info,
    > > const char *name) { }
    > > +static inline int ptdump_check_wx_init(void) { return 0; }
    > > #endif
    > > void ptdump_check_wx(void);
    > > #endif /* CONFIG_PTDUMP_CORE */
    > > diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
    > > index 860c00ec8bd3..60c99a047763 100644
    > > --- a/arch/arm64/mm/dump.c
    > > +++ b/arch/arm64/mm/dump.c
    > > @@ -378,6 +378,7 @@ static int ptdump_init(void)
    > > #endif
    > > ptdump_initialize();
    > > ptdump_debugfs_register(&kernel_ptdump_info, "kernel_page_tables");
    > > + ptdump_check_wx_init();
    > > return 0;
    > > }
    > > device_initcall(ptdump_init);
    > > diff --git a/arch/arm64/mm/ptdump_debugfs.c b/arch/arm64/mm/ptdump_debugfs.c
    > > index 1f2eae3e988b..73cddc12c3c2 100644
    > > --- a/arch/arm64/mm/ptdump_debugfs.c
    > > +++ b/arch/arm64/mm/ptdump_debugfs.c
    > > @@ -16,3 +16,21 @@ void ptdump_debugfs_register(struct ptdump_info *info, const char *name)
    > > {
    > > debugfs_create_file(name, 0400, NULL, info, &ptdump_fops);
    > > }
    > > +
    > > +static int check_wx_debugfs_set(void *data, u64 val)
    > > +{
    > > + if (val != 1ULL)
    > > + return -EINVAL;
    > > +
    > > + ptdump_check_wx();
    > > +
    > > + return 0;
    > > +}
    > > +
    > > +DEFINE_SIMPLE_ATTRIBUTE(check_wx_fops, NULL, check_wx_debugfs_set, "%llu\n");
    > > +
    > > +int ptdump_check_wx_init(void)
    > > +{
    > > + return debugfs_create_file("check_wx_pages", 0200, NULL,
    > > + NULL, &check_wx_fops) ? 0 : -ENOMEM;

    Do not check the return value of this function, especially as it is
    returning a pointer, not an int!

    Just call the function and move on, you should not do anything different
    if it returns an error or not.

    thanks,
    greg k-h

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