diff mbox series

[PULL,07/23] bsd-user/mmap.c: Don't mmap fd == -1 independently from MAP_ANON flag

Message ID 20211018160458.1976-8-imp@bsdimp.com (mailing list archive)
State New, archived
Headers show
Series [PULL,01/23] bsd-user/mmap.c: Always zero MAP_ANONYMOUS memory in mmap_frag() | expand

Commit Message

Warner Losh Oct. 18, 2021, 4:04 p.m. UTC 
From: Guy Yur <guyyur@gmail.com>

Switch checks for !(flags & MAP_ANONYMOUS) with checks for fd != -1.
MAP_STACK and MAP_GUARD both require fd == -1 and don't require mapping
the fd either. Add analysis from Guy Yur detailing the different cases
for MAP_GUARD and MAP_STACK.

Signed-off-by: Guy Yur <guyyur@gmail.com>
[ partially merged before, finishing the job and documenting origin]
Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Kyle Evans <kevans@FreeBSD.org>
---
 bsd-user/mmap.c   | 30 +++++++++++++++++++++++++-----
 roms/seabios-hppa |  2 +-
 2 files changed, 26 insertions(+), 6 deletions(-)

Comments

Richard Henderson Oct. 18, 2021, 6:45 p.m. UTC | #1 
On 10/18/21 9:04 AM, Warner Losh wrote:
> diff --git a/roms/seabios-hppa b/roms/seabios-hppa
> index b12acac4be..73b740f771 160000
> --- a/roms/seabios-hppa
> +++ b/roms/seabios-hppa
> @@ -1 +1 @@
> -Subproject commit b12acac4be27b6d5d9fbe48c4be1286dcc245fbb
> +Subproject commit 73b740f77190643b2ada5ee97a9a108c6ef2a37b

You rebased with a stale submodule.
You'll need to fix that and recreate the pull request.



r~
Warner Losh Oct. 18, 2021, 6:47 p.m. UTC | #2 
On Mon, Oct 18, 2021 at 12:45 PM Richard Henderson <
richard.henderson@linaro.org> wrote:

> On 10/18/21 9:04 AM, Warner Losh wrote:
> > diff --git a/roms/seabios-hppa b/roms/seabios-hppa
> > index b12acac4be..73b740f771 160000
> > --- a/roms/seabios-hppa
> > +++ b/roms/seabios-hppa
> > @@ -1 +1 @@
> > -Subproject commit b12acac4be27b6d5d9fbe48c4be1286dcc245fbb
> > +Subproject commit 73b740f77190643b2ada5ee97a9a108c6ef2a37b
>
> You rebased with a stale submodule.
> You'll need to fix that and recreate the pull request.
>

Doh! I tried really hard *NOT* to do that.

So is this PULL v2 then?

Warner
Richard Henderson Oct. 18, 2021, 6:48 p.m. UTC | #3 
On 10/18/21 11:47 AM, Warner Losh wrote:
> 
> 
> On Mon, Oct 18, 2021 at 12:45 PM Richard Henderson <richard.henderson@linaro.org 
> <mailto:richard.henderson@linaro.org>> wrote:
> 
>     On 10/18/21 9:04 AM, Warner Losh wrote:
>      > diff --git a/roms/seabios-hppa b/roms/seabios-hppa
>      > index b12acac4be..73b740f771 160000
>      > --- a/roms/seabios-hppa
>      > +++ b/roms/seabios-hppa
>      > @@ -1 +1 @@
>      > -Subproject commit b12acac4be27b6d5d9fbe48c4be1286dcc245fbb
>      > +Subproject commit 73b740f77190643b2ada5ee97a9a108c6ef2a37b
> 
>     You rebased with a stale submodule.
>     You'll need to fix that and recreate the pull request.
> 
> 
> Doh! I tried really hard *NOT* to do that.
> 
> So is this PULL v2 then?

Yep.

r~
diff mbox series

Patch

diff --git a/bsd-user/mmap.c b/bsd-user/mmap.c
index face98573f..4ecd949a10 100644
--- a/bsd-user/mmap.c
+++ b/bsd-user/mmap.c
@@ -127,7 +127,27 @@  error:
     return ret;
 }
 
-/* map an incomplete host page */
+/*
+ * map an incomplete host page
+ *
+ * mmap_frag can be called with a valid fd, if flags doesn't contain one of
+ * MAP_ANON, MAP_STACK, MAP_GUARD. If we need to map a page in those cases, we
+ * pass fd == -1. However, if flags contains MAP_GUARD then MAP_ANON cannot be
+ * added.
+ *
+ * * If fd is valid (not -1) we want to map the pages with MAP_ANON.
+ * * If flags contains MAP_GUARD we don't want to add MAP_ANON because it
+ *   will be rejected.  See kern_mmap's enforcing of constraints for MAP_GUARD
+ *   in sys/vm/vm_mmap.c.
+ * * If flags contains MAP_ANON it doesn't matter if we add it or not.
+ * * If flags contains MAP_STACK, mmap adds MAP_ANON when called so doesn't
+ *   matter if we add it or not either. See enforcing of constraints for
+ *   MAP_STACK in kern_mmap.
+ *
+ * Don't add MAP_ANON for the flags that use fd == -1 without specifying the
+ * flags directly, with the assumption that future flags that require fd == -1
+ * will also not require MAP_ANON.
+ */
 static int mmap_frag(abi_ulong real_start,
                      abi_ulong start, abi_ulong end,
                      int prot, int flags, int fd, abi_ulong offset)
@@ -147,9 +167,9 @@  static int mmap_frag(abi_ulong real_start,
     }
 
     if (prot1 == 0) {
-        /* no page was there, so we allocate one */
+        /* no page was there, so we allocate one. See also above. */
         void *p = mmap(host_start, qemu_host_page_size, prot,
-                       flags | MAP_ANON, -1, 0);
+                       flags | ((fd != -1) ? MAP_ANON : 0), -1, 0);
         if (p == MAP_FAILED)
             return -1;
         prot1 = prot;
@@ -157,7 +177,7 @@  static int mmap_frag(abi_ulong real_start,
     prot1 &= PAGE_BITS;
 
     prot_new = prot | prot1;
-    if (!(flags & MAP_ANON)) {
+    if (fd != -1) {
         /* msync() won't work here, so we return an error if write is
            possible while it is a shared mapping */
         if ((flags & TARGET_BSD_MAP_FLAGMASK) == MAP_SHARED &&
@@ -565,7 +585,7 @@  abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
          * worst case: we cannot map the file because the offset is not
          * aligned, so we read it
          */
-        if (!(flags & MAP_ANON) &&
+        if (fd != -1 &&
             (offset & ~qemu_host_page_mask) != (start & ~qemu_host_page_mask)) {
             /*
              * msync() won't work here, so we return an error if write is
diff --git a/roms/seabios-hppa b/roms/seabios-hppa
index b12acac4be..73b740f771 160000
--- a/roms/seabios-hppa
+++ b/roms/seabios-hppa
@@ -1 +1 @@ 
-Subproject commit b12acac4be27b6d5d9fbe48c4be1286dcc245fbb
+Subproject commit 73b740f77190643b2ada5ee97a9a108c6ef2a37b