powerpc/ptrace: Simplify gpr_get()/tm_cgpr_get()

gpr_get() does membuf_write() twice to override pt_regs->msr in
between. We can call membuf_write() once and change ->msr in the
kernel buffer, this simplifies the code and the next fix.

The patch adds a new simple helper, membuf_at(offs), it returns the
new membuf which can be safely used after membuf_write().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
[mpe: Fixup some minor whitespace issues noticed by Christophe]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201119160221.GA5188@redhat.com

diff --git a/arch/powerpc/kernel/ptrace/ptrace-tm.c b/arch/powerpc/kernel/ptrace/ptrace-tm.c
index 54f2d07..f15cbba 100644 (file)
--- a/arch/powerpc/kernel/ptrace/ptrace-tm.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-tm.c
@@ -86,6 +86,8 @@ int tm_cgpr_active(struct task_struct *target, const struct user_regset *regset)
 int tm_cgpr_get(struct task_struct *target, const struct user_regset *regset,
                struct membuf to)
 {
+       struct membuf to_msr = membuf_at(&to, offsetof(struct pt_regs, msr));
+
        if (!cpu_has_feature(CPU_FTR_TM))
                return -ENODEV;
 
@@ -96,16 +98,10 @@ int tm_cgpr_get(struct task_struct *target, const struct user_regset *regset,
        flush_fp_to_thread(target);
        flush_altivec_to_thread(target);
 
-       membuf_write(&to, &target->thread.ckpt_regs,
-                       offsetof(struct pt_regs, msr));
-       membuf_store(&to, get_user_ckpt_msr(target));
+       membuf_write(&to, &target->thread.ckpt_regs, sizeof(struct user_pt_regs));
 
-       BUILD_BUG_ON(offsetof(struct pt_regs, orig_gpr3) !=
-                    offsetof(struct pt_regs, msr) + sizeof(long));
+       membuf_store(&to_msr, get_user_ckpt_msr(target));
 
-       membuf_write(&to, &target->thread.ckpt_regs.orig_gpr3,
-                       sizeof(struct user_pt_regs) -
-                       offsetof(struct pt_regs, orig_gpr3));
        return membuf_zero(&to, ELF_NGREG * sizeof(unsigned long) -
                        sizeof(struct user_pt_regs));
 }

diff --git a/arch/powerpc/kernel/ptrace/ptrace-view.c b/arch/powerpc/kernel/ptrace/ptrace-view.c
index 7e6478e..299e0b6 100644 (file)
--- a/arch/powerpc/kernel/ptrace/ptrace-view.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-view.c
@@ -217,6 +217,7 @@ int ptrace_put_reg(struct task_struct *task, int regno, unsigned long data)
 static int gpr_get(struct task_struct *target, const struct user_regset *regset,
                   struct membuf to)
 {
+       struct membuf to_msr = membuf_at(&to, offsetof(struct pt_regs, msr));
        int i;
 
        if (target->thread.regs == NULL)
@@ -228,15 +229,10 @@ static int gpr_get(struct task_struct *target, const struct user_regset *regset,
                        target->thread.regs->gpr[i] = NV_REG_POISON;
        }
 
-       membuf_write(&to, target->thread.regs, offsetof(struct pt_regs, msr));
-       membuf_store(&to, get_user_msr(target));
+       membuf_write(&to, target->thread.regs, sizeof(struct user_pt_regs));
 
-       BUILD_BUG_ON(offsetof(struct pt_regs, orig_gpr3) !=
-                    offsetof(struct pt_regs, msr) + sizeof(long));
+       membuf_store(&to_msr, get_user_msr(target));
 
-       membuf_write(&to, &target->thread.regs->orig_gpr3,
-                       sizeof(struct user_pt_regs) -
-                       offsetof(struct pt_regs, orig_gpr3));
        return membuf_zero(&to, ELF_NGREG * sizeof(unsigned long) -
                                 sizeof(struct user_pt_regs));
 }

diff --git a/include/linux/regset.h b/include/linux/regset.h
index c3403f3..a00765f 100644 (file)
--- a/include/linux/regset.h
+++ b/include/linux/regset.h
@@ -46,6 +46,18 @@ static inline int membuf_write(struct membuf *s, const void *v, size_t size)
        return s->left;
 }
 
+static inline struct membuf membuf_at(const struct membuf *s, size_t offs)
+{
+       struct membuf n = *s;
+
+       if (offs > n.left)
+               offs = n.left;
+       n.p += offs;
+       n.left -= offs;
+
+       return n;
+}
+
 /* current s->p must be aligned for v; v must be a scalar */
 #define membuf_store(s, v)                             \
 ({                                                     \