On Thu, 2 Aug 2012, James Bottomley wrote:
> > In case of parsic, let's take a process with current->personality ==
> > PER_LINUX32 callling personality(PER_LINUX | UNAME26). The
> >
> > if (personality(current->personality) == PER_LINUX32
> > && personality == PER_LINUX)
> > personality = PER_LINUX32;
> >
> > would that have no effect, and sys_personality() would be called with
> > (PER_LINUX | UNAME26) instead of PER_LINUX32, just because of UNAME26
> > being set as well. That doesn't seem really correct. Is it?
>
> Heh, no. This is a nasty mess.
Indeed.
> Our assumption was that we own the flags ... hence the code. There are
> some flags we can't allow to be set or reset ... but that's only for the
> mythical 64 bit userspace, so I suppose we just ignore that for now and
> fix it if this ever appears.
>
> I don't like the hidden assumption that PER_LINUX == 0, but otherwise
> the code looks fine.
>
> How about
>
> personality = (personality & ~PER_MASK) | PER_LINUX32;
>
> and
>
> err = (personality & ~PER_MASK) | PER_LINUX;
Agreed, that's a little bit nicer way how to express it (modulo the
fact that the last 'personality' in your example should in fact be 'err').
Updated patch below, thanks.
From: Jiri Kosina <jkosina@xxxxxxx>
Subject: [PATCH 2/4] parisc: fix personality flag check in copy_thread()
Directly comparing task_struct->personality against PER_* is not fully
correct, as it doesn't take flags potentially stored in top three bytes
into account.
Analogically, directly forcefully setting personality to PER_LINUX32 or
PER_LINUX discards any flags stored in the top three bytes.
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
---
v0->v1: fix the bit ops to reflect the fact that PER_LINUX is actually 0
v2->v2: express the PER_LINUX==0 fact in the bitops in a more obvious way
arch/parisc/kernel/process.c | 2 +-
arch/parisc/kernel/sys_parisc.c | 8 ++++----
2 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
index d4b94b3..2c05a92 100644
--- a/arch/parisc/kernel/process.c
+++ b/arch/parisc/kernel/process.c
@@ -309,7 +309,7 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
cregs->ksp = (unsigned long)stack
+ (pregs->gr[21] & (THREAD_SIZE - 1));
cregs->gr[30] = usp;
- if (p->personality == PER_HPUX) {
+ if (personality(p->personality) == PER_HPUX) {
#ifdef CONFIG_HPUX
cregs->kpc = (unsigned long) &hpux_child_return;
#else
diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
index c9b9322..7f9658e 100644
--- a/arch/parisc/kernel/sys_parisc.c
+++ b/arch/parisc/kernel/sys_parisc.c
@@ -225,12 +225,12 @@ long parisc_personality(unsigned long personality)
long err;
if (personality(current->personality) == PER_LINUX32
- && personality == PER_LINUX)
- personality = PER_LINUX32;
+ && personality(personality) == PER_LINUX)
+ personality = (personality & ~PER_MASK) | PER_LINUX32;
err = sys_personality(personality);
- if (err == PER_LINUX32)
- err = PER_LINUX;
+ if (personality(err) == PER_LINUX32)
+ err = (err & ~PER_MASK) | PER_LINUX;
return err;
}
--
Jiri Kosina
SUSE Labs
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