Commit-ID: b81ff1013eb8eef2934ca7e8cf53d553c1029e84 Gitweb: https://git.kernel.org/tip/b81ff1013eb8eef2934ca7e8cf53d553c1029e84 Author: Hugh Dickins <hughd@xxxxxxxxxx> AuthorDate: Wed, 29 May 2019 09:25:40 +0200 Committer: Borislav Petkov <bp@xxxxxxx> CommitDate: Thu, 6 Jun 2019 19:15:17 +0200 x86/fpu: Use fault_in_pages_writeable() for pre-faulting Since commit d9c9ce34ed5c8 ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails") get_user_pages_unlocked() pre-faults user's memory if a write generates a page fault while the handler is disabled. This works in general and uncovered a bug as reported by Mike Rapoport¹. It has been pointed out that this function may be fragile and a simple pre-fault as in fault_in_pages_writeable() would be a better solution. Better as in taste and simplicity: that write (as performed by the alternative function) performs exactly the same faulting of memory as before. This was suggested by Hugh Dickins and Andrew Morton. Use fault_in_pages_writeable() for pre-faulting user's stack. [ bigeasy: Write commit message. ] [ bp: Massage some. ] ¹ https://lkml.kernel.org/r/1557844195-18882-1-git-send-email-rppt@xxxxxxxxxxxxx Fixes: d9c9ce34ed5c8 ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails") Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Tested-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: linux-mm <linux-mm@xxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx> Cc: Pavel Machek <pavel@xxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: x86-ml <x86@xxxxxxxxxx> Link: https://lkml.kernel.org/r/20190529072540.g46j4kfeae37a3iu@xxxxxxxxxxxxx Link: https://lkml.kernel.org/r/1557844195-18882-1-git-send-email-rppt@xxxxxxxxxxxxx --- arch/x86/kernel/fpu/signal.c | 11 ++--------- 1 file changed, 2 insertions(+), 9 deletions(-) diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c index 5a8d118bc423..060d6188b453 100644 --- a/arch/x86/kernel/fpu/signal.c +++ b/arch/x86/kernel/fpu/signal.c @@ -5,6 +5,7 @@ #include <linux/compat.h> #include <linux/cpu.h> +#include <linux/pagemap.h> #include <asm/fpu/internal.h> #include <asm/fpu/signal.h> @@ -189,15 +190,7 @@ retry: fpregs_unlock(); if (ret) { - int aligned_size; - int nr_pages; - - aligned_size = offset_in_page(buf_fx) + fpu_user_xstate_size; - nr_pages = DIV_ROUND_UP(aligned_size, PAGE_SIZE); - - ret = get_user_pages_unlocked((unsigned long)buf_fx, nr_pages, - NULL, FOLL_WRITE); - if (ret == nr_pages) + if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size)) goto retry; return -EFAULT; }
