Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull core kernel fixes from Ingo Molnar:
 "This is mostly the copy_to_user_mcsafe() related fixes from Dan
  Williams, and an ORC fix for Clang"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/asm/memcpy_mcsafe: Fix copy_to_user_mcsafe() exception handling
  lib/iov_iter: Fix pipe handling in _copy_to_iter_mcsafe()
  lib/iov_iter: Document _copy_to_iter_flushcache()
  lib/iov_iter: Document _copy_to_iter_mcsafe()
  objtool: Use '.strtab' if '.shstrtab' doesn't exist, to support ORC tables on Clang

4 files changed, 84 insertions, 8 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f1dbb4ee19d7..887d3a7bb646 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -63,7 +63,7 @@ config X86
         select ARCH_HAS_PTE_SPECIAL
         select ARCH_HAS_REFCOUNT
         select ARCH_HAS_UACCESS_FLUSHCACHE      if X86_64
-        select ARCH_HAS_UACCESS_MCSAFE          if X86_64
+        select ARCH_HAS_UACCESS_MCSAFE          if X86_64 && X86_MCE
         select ARCH_HAS_SET_MEMORY
         select ARCH_HAS_SG_CHAIN
         select ARCH_HAS_STRICT_KERNEL_RWX
diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
index 62acb613114b..a9d637bc301d 100644
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -52,7 +52,12 @@ copy_to_user_mcsafe(void *to, const void *from, unsigned len)
         unsigned long ret;
 
         __uaccess_begin();
-        ret = memcpy_mcsafe(to, from, len);
+        /*
+         * Note, __memcpy_mcsafe() is explicitly used since it can
+         * handle exceptions / faults.  memcpy_mcsafe() may fall back to
+         * memcpy() which lacks this handling.
+         */
+        ret = __memcpy_mcsafe(to, from, len);
         __uaccess_end();
         return ret;
 }
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 7e43cd54c84c..8be175df3075 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -596,15 +596,70 @@ static unsigned long memcpy_mcsafe_to_page(struct page *page, size_t offset,
         return ret;
 }
 
+static size_t copy_pipe_to_iter_mcsafe(const void *addr, size_t bytes,
+                                struct iov_iter *i)
+{
+        struct pipe_inode_info *pipe = i->pipe;
+        size_t n, off, xfer = 0;
+        int idx;
+
+        if (!sanity(i))
+                return 0;
+
+        bytes = n = push_pipe(i, bytes, &idx, &off);
+        if (unlikely(!n))
+                return 0;
+        for ( ; n; idx = next_idx(idx, pipe), off = 0) {
+                size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
+                unsigned long rem;
+
+                rem = memcpy_mcsafe_to_page(pipe->bufs[idx].page, off, addr,
+                                chunk);
+                i->idx = idx;
+                i->iov_offset = off + chunk - rem;
+                xfer += chunk - rem;
+                if (rem)
+                        break;
+                n -= chunk;
+                addr += chunk;
+        }
+        i->count -= xfer;
+        return xfer;
+}
+
+/**
+ * _copy_to_iter_mcsafe - copy to user with source-read error exception handling
+ * @addr: source kernel address
+ * @bytes: total transfer length
+ * @iter: destination iterator
+ *
+ * The pmem driver arranges for filesystem-dax to use this facility via
+ * dax_copy_to_iter() for protecting read/write to persistent memory.
+ * Unless / until an architecture can guarantee identical performance
+ * between _copy_to_iter_mcsafe() and _copy_to_iter() it would be a
+ * performance regression to switch more users to the mcsafe version.
+ *
+ * Otherwise, the main differences between this and typical _copy_to_iter().
+ *
+ * * Typical tail/residue handling after a fault retries the copy
+ *   byte-by-byte until the fault happens again. Re-triggering machine
+ *   checks is potentially fatal so the implementation uses source
+ *   alignment and poison alignment assumptions to avoid re-triggering
+ *   hardware exceptions.
+ *
+ * * ITER_KVEC, ITER_PIPE, and ITER_BVEC can return short copies.
+ *   Compare to copy_to_iter() where only ITER_IOVEC attempts might return
+ *   a short copy.
+ *
+ * See MCSAFE_TEST for self-test.
+ */
 size_t _copy_to_iter_mcsafe(const void *addr, size_t bytes, struct iov_iter *i)
 {
         const char *from = addr;
         unsigned long rem, curr_addr, s_addr = (unsigned long) addr;
 
-        if (unlikely(i->type & ITER_PIPE)) {
-                WARN_ON(1);
-                return 0;
-        }
+        if (unlikely(i->type & ITER_PIPE))
+                return copy_pipe_to_iter_mcsafe(addr, bytes, i);
         if (iter_is_iovec(i))
                 might_fault();
         iterate_and_advance(i, bytes, v,
@@ -701,6 +756,20 @@ size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
 EXPORT_SYMBOL(_copy_from_iter_nocache);
 
 #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
+/**
+ * _copy_from_iter_flushcache - write destination through cpu cache
+ * @addr: destination kernel address
+ * @bytes: total transfer length
+ * @iter: source iterator
+ *
+ * The pmem driver arranges for filesystem-dax to use this facility via
+ * dax_copy_from_iter() for ensuring that writes to persistent memory
+ * are flushed through the CPU cache. It is differentiated from
+ * _copy_from_iter_nocache() in that guarantees all data is flushed for
+ * all iterator types. The _copy_from_iter_nocache() only attempts to
+ * bypass the cache for the ITER_IOVEC case, and on some archs may use
+ * instructions that strand dirty-data in the cache.
+ */
 size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
 {
         char *to = addr;
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 0d1acb704f64..7ec85d567598 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -519,10 +519,12 @@ struct section *elf_create_section(struct elf *elf, const char *name,
         sec->sh.sh_flags = SHF_ALLOC;
 
 
-        /* Add section name to .shstrtab */
+        /* Add section name to .shstrtab (or .strtab for Clang) */
         shstrtab = find_section_by_name(elf, ".shstrtab");
+        if (!shstrtab)
+                shstrtab = find_section_by_name(elf, ".strtab");
         if (!shstrtab) {
-                WARN("can't find .shstrtab section");
+                WARN("can't find .shstrtab or .strtab section");
                 return NULL;
         }