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Subject[RFC][PATCH v2 16/22] x86: get rid of put_user_try in __setup_rt_frame() (both 32bit and 64bit)
Date
From: Al Viro <viro@zeniv.linux.org.uk>

Straightforward, except for save_altstack_ex() stuck in those.
Replace that thing with an analogue that would use unsafe_put_user()
instead of put_user_ex() (called compat_save_altstack()) and be done
with that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
arch/x86/kernel/signal.c | 91 +++++++++++++++++++++++++-----------------------
include/linux/signal.h | 8 ++---
2 files changed, 52 insertions(+), 47 deletions(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 29abad29aaa1..8b879fdc214c 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -365,38 +365,37 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,

frame = get_sigframe(&ksig->ka, regs, sizeof(*frame), &fpstate);

- if (!access_ok(frame, sizeof(*frame)))
+ if (!user_access_begin(frame, sizeof(*frame)))
return -EFAULT;

- put_user_try {
- put_user_ex(sig, &frame->sig);
- put_user_ex(&frame->info, &frame->pinfo);
- put_user_ex(&frame->uc, &frame->puc);
+ unsafe_put_user(sig, &frame->sig, Efault);
+ unsafe_put_user(&frame->info, &frame->pinfo, Efault);
+ unsafe_put_user(&frame->uc, &frame->puc, Efault);

- /* Create the ucontext. */
- if (static_cpu_has(X86_FEATURE_XSAVE))
- put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags);
- else
- put_user_ex(0, &frame->uc.uc_flags);
- put_user_ex(0, &frame->uc.uc_link);
- save_altstack_ex(&frame->uc.uc_stack, regs->sp);
+ /* Create the ucontext. */
+ if (static_cpu_has(X86_FEATURE_XSAVE))
+ unsafe_put_user(UC_FP_XSTATE, &frame->uc.uc_flags, Efault);
+ else
+ unsafe_put_user(0, &frame->uc.uc_flags, Efault);
+ unsafe_put_user(0, &frame->uc.uc_link, Efault);
+ unsafe_save_altstack(&frame->uc.uc_stack, regs->sp, Efault);

- /* Set up to return from userspace. */
- restorer = current->mm->context.vdso +
- vdso_image_32.sym___kernel_rt_sigreturn;
- if (ksig->ka.sa.sa_flags & SA_RESTORER)
- restorer = ksig->ka.sa.sa_restorer;
- put_user_ex(restorer, &frame->pretcode);
+ /* Set up to return from userspace. */
+ restorer = current->mm->context.vdso +
+ vdso_image_32.sym___kernel_rt_sigreturn;
+ if (ksig->ka.sa.sa_flags & SA_RESTORER)
+ restorer = ksig->ka.sa.sa_restorer;
+ unsafe_put_user(restorer, &frame->pretcode, Efault);

- /*
- * This is movl $__NR_rt_sigreturn, %ax ; int $0x80
- *
- * WE DO NOT USE IT ANY MORE! It's only left here for historical
- * reasons and because gdb uses it as a signature to notice
- * signal handler stack frames.
- */
- put_user_ex(*((u64 *)&rt_retcode), (u64 *)frame->retcode);
- } put_user_catch(err);
+ /*
+ * This is movl $__NR_rt_sigreturn, %ax ; int $0x80
+ *
+ * WE DO NOT USE IT ANY MORE! It's only left here for historical
+ * reasons and because gdb uses it as a signature to notice
+ * signal handler stack frames.
+ */
+ unsafe_put_user(*((u64 *)&rt_retcode), (u64 *)frame->retcode, Efault);
+ user_access_end();

err |= copy_siginfo_to_user(&frame->info, &ksig->info);
err |= setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
@@ -419,6 +418,9 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
regs->cs = __USER_CS;

return 0;
+Efault:
+ user_access_end();
+ return -EFAULT;
}
#else /* !CONFIG_X86_32 */
static unsigned long frame_uc_flags(struct pt_regs *regs)
@@ -444,6 +446,10 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
unsigned long uc_flags;
int err = 0;

+ /* x86-64 should always use SA_RESTORER. */
+ if (!(ksig->ka.sa.sa_flags & SA_RESTORER))
+ return -EFAULT;
+
frame = get_sigframe(&ksig->ka, regs, sizeof(struct rt_sigframe), &fp);

if (!access_ok(frame, sizeof(*frame)))
@@ -455,23 +461,18 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
}

uc_flags = frame_uc_flags(regs);
+ if (!user_access_begin(frame, sizeof(*frame)))
+ return -EFAULT;

- put_user_try {
- /* Create the ucontext. */
- put_user_ex(uc_flags, &frame->uc.uc_flags);
- put_user_ex(0, &frame->uc.uc_link);
- save_altstack_ex(&frame->uc.uc_stack, regs->sp);
-
- /* Set up to return from userspace. If provided, use a stub
- already in userspace. */
- /* x86-64 should always use SA_RESTORER. */
- if (ksig->ka.sa.sa_flags & SA_RESTORER) {
- put_user_ex(ksig->ka.sa.sa_restorer, &frame->pretcode);
- } else {
- /* could use a vstub here */
- err |= -EFAULT;
- }
- } put_user_catch(err);
+ /* Create the ucontext. */
+ unsafe_put_user(uc_flags, &frame->uc.uc_flags, Efault);
+ unsafe_put_user(0, &frame->uc.uc_link, Efault);
+ unsafe_save_altstack(&frame->uc.uc_stack, regs->sp, Efault);
+
+ /* Set up to return from userspace. If provided, use a stub
+ already in userspace. */
+ unsafe_put_user(ksig->ka.sa.sa_restorer, &frame->pretcode, Efault);
+ user_access_end();

err |= setup_sigcontext(&frame->uc.uc_mcontext, fp, regs, set->sig[0]);
err |= __put_user(set->sig[0], &frame->uc.uc_sigmask.sig[0]);
@@ -515,6 +516,10 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
force_valid_ss(regs);

return 0;
+
+Efault:
+ user_access_end();
+ return -EFAULT;
}
#endif /* CONFIG_X86_32 */

diff --git a/include/linux/signal.h b/include/linux/signal.h
index 1a5f88316b08..05bacd2ab135 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -444,12 +444,12 @@ void signals_init(void);
int restore_altstack(const stack_t __user *);
int __save_altstack(stack_t __user *, unsigned long);

-#define save_altstack_ex(uss, sp) do { \
+#define unsafe_save_altstack(uss, sp, label) do { \
stack_t __user *__uss = uss; \
struct task_struct *t = current; \
- put_user_ex((void __user *)t->sas_ss_sp, &__uss->ss_sp); \
- put_user_ex(t->sas_ss_flags, &__uss->ss_flags); \
- put_user_ex(t->sas_ss_size, &__uss->ss_size); \
+ unsafe_put_user((void __user *)t->sas_ss_sp, &__uss->ss_sp, label); \
+ unsafe_put_user(t->sas_ss_flags, &__uss->ss_flags, label); \
+ unsafe_put_user(t->sas_ss_size, &__uss->ss_size, label); \
if (t->sas_ss_flags & SS_AUTODISARM) \
sas_ss_reset(t); \
} while (0);
--
2.11.0
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