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    SubjectRe: [PATCH v2] powerpc/signal32: Use fault_in_pages_readable() to prefault user context
    On Tue, Apr 24, 2018 at 6:04 PM, Christophe Leroy
    <christophe.leroy@c-s.fr> wrote:
    > Use fault_in_pages_readable() to prefault user context
    > instead of open coding
    >
    > Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
    > ---
    > v2: using sizeof(*ctx) as size of ctx instead of 1
    >
    > arch/powerpc/kernel/signal_32.c | 13 +++++--------
    > 1 file changed, 5 insertions(+), 8 deletions(-)
    >
    > diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
    > index 492f03451877..4a9e4d6d555b 100644
    > --- a/arch/powerpc/kernel/signal_32.c
    > +++ b/arch/powerpc/kernel/signal_32.c
    > @@ -25,6 +25,7 @@
    > #include <linux/errno.h>
    > #include <linux/elf.h>
    > #include <linux/ptrace.h>
    > +#include <linux/pagemap.h>
    > #include <linux/ratelimit.h>
    > #ifdef CONFIG_PPC64
    > #include <linux/syscalls.h>
    > @@ -1045,7 +1046,6 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
    > struct ucontext __user *new_ctx,
    > int ctx_size, int r6, int r7, int r8, struct pt_regs *regs)
    > {
    > - unsigned char tmp __maybe_unused;
    > int ctx_has_vsx_region = 0;
    >
    > #ifdef CONFIG_PPC64
    > @@ -1109,9 +1109,8 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
    > }
    > if (new_ctx == NULL)
    > return 0;
    > - if (!access_ok(VERIFY_READ, new_ctx, ctx_size)
    > - || __get_user(tmp, (u8 __user *) new_ctx)
    > - || __get_user(tmp, (u8 __user *) new_ctx + ctx_size - 1))
    > + if (!access_ok(VERIFY_READ, new_ctx, ctx_size) ||
    > + fault_in_pages_readable((u8 __user *)new_ctx, ctx_size))
    > return -EFAULT;
    >
    > /*
    > @@ -1231,7 +1230,6 @@ int sys_debug_setcontext(struct ucontext __user *ctx,
    > {
    > struct sig_dbg_op op;
    > int i;
    > - unsigned char tmp __maybe_unused;
    > unsigned long new_msr = regs->msr;
    > #ifdef CONFIG_PPC_ADV_DEBUG_REGS
    > unsigned long new_dbcr0 = current->thread.debug.dbcr0;
    > @@ -1287,9 +1285,8 @@ int sys_debug_setcontext(struct ucontext __user *ctx,
    > current->thread.debug.dbcr0 = new_dbcr0;
    > #endif
    >
    > - if (!access_ok(VERIFY_READ, ctx, sizeof(*ctx))
    > - || __get_user(tmp, (u8 __user *) ctx)
    > - || __get_user(tmp, (u8 __user *) (ctx + 1) - 1))
    > + if (!access_ok(VERIFY_READ, ctx, sizeof(*ctx)) ||
    > + fault_in_pages_readable((u8 __user *)ctx, sizeof(*ctx)))
    > return -EFAULT;
    >
    > /*
    > --
    > 2.13.3
    >


    Looks good:

    Reviewed-by: Mathieu Malaterre <malat@debian.org>

    Thanks for fixing my previous attempt !

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