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charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, Apr 16, 2021 at 02:34:41PM +0100, Mark Rutland wrote: > On Fri, Apr 16, 2021 at 01:33:22PM +0100, Catalin Marinas wrote: > > On Fri, Apr 16, 2021 at 03:55:31PM +0800, He Zhe wrote: > > > The general version of is_syscall_success does not handle 32-bit > > > compatible case, which would cause 32-bit negative return code to be > > > recoganized as a positive number later and seen as a "success". > > > > > > Since is_compat_thread is defined in compat.h, implementing > > > is_syscall_success in ptrace.h would introduce build failure due to > > > recursive inclusion of some basic headers like mutex.h. We put the > > > implementation to ptrace.c > > > > > > Signed-off-by: He Zhe > > > --- > > > arch/arm64/include/asm/ptrace.h | 3 +++ > > > arch/arm64/kernel/ptrace.c | 10 ++++++++++ > > > 2 files changed, 13 insertions(+) > > > > > > diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h > > > index e58bca832dff..3c415e9e5d85 100644 > > > --- a/arch/arm64/include/asm/ptrace.h > > > +++ b/arch/arm64/include/asm/ptrace.h > > > @@ -328,6 +328,9 @@ static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc) > > > regs->regs[0] = rc; > > > } > > > > > > +extern inline int is_syscall_success(struct pt_regs *regs); > > > +#define is_syscall_success(regs) is_syscall_success(regs) > > > + > > > /** > > > * regs_get_kernel_argument() - get Nth function argument in kernel > > > * @regs: pt_regs of that context > > > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c > > > index 170f42fd6101..3266201f8c60 100644 > > > --- a/arch/arm64/kernel/ptrace.c > > > +++ b/arch/arm64/kernel/ptrace.c > > > @@ -1909,3 +1909,13 @@ int valid_user_regs(struct user_pt_regs *regs, struct task_struct *task) > > > else > > > return valid_native_regs(regs); > > > } > > > + > > > +inline int is_syscall_success(struct pt_regs *regs) > > > +{ > > > + unsigned long val = regs->regs[0]; > > > + > > > + if (is_compat_thread(task_thread_info(current))) > > > + val = sign_extend64(val, 31); > > > + > > > + return !IS_ERR_VALUE(val); > > > +} > > > > It's better to use compat_user_mode(regs) here instead of > > is_compat_thread(). It saves us from worrying whether regs are for the > > current context. > > > > I think we should change regs_return_value() instead. This function > > seems to be called from several other places and it has the same > > potential problems if called on compat pt_regs. > > I think this is a problem we created for ourselves back in commit: > > 15956689a0e60aa0 ("arm64: compat: Ensure upper 32 bits of x0 are zero on syscall return) > > AFAICT, the perf regs samples are the only place this matters, since for > ptrace the compat regs are implicitly truncated to compat_ulong_t, and > audit expects the non-truncated return value. Other architectures don't > truncate here, so I think we're setting ourselves up for a game of > whack-a-mole to truncate and extend wherever we need to. > > Given that, I suspect it'd be better to do something like the below. > > Will, thoughts? I think perf is one example, but this is also visible to userspace via the native ptrace interface and I distinctly remember needing this for some versions of arm64 strace to work correctly when tracing compat tasks. So I do think that clearing the upper bits on the return path is the right approach, but it sounds like we need some more work to handle syscall(-1) and audit (what exactly is the problem here after these patches have been applied?) Will -- Linux-audit mailing list Linux-audit@redhat.com https://listman.redhat.com/mailman/listinfo/linux-audit