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* [RFC PATCH v2] linux-user: Use FD_32BIT_MODE fd flag for 32-bit guests
@ 2020-06-23 10:01 Peter Maydell
  2020-06-23 14:57 ` Laurent Vivier
  0 siblings, 1 reply; 3+ messages in thread
From: Peter Maydell @ 2020-06-23 10:01 UTC (permalink / raw)
  To: qemu-devel; +Cc: Linus Walleij, Riku Voipio, Laurent Vivier

If the guest is 32 bit then there is a potential problem if the
host gives us back a 64-bit sized value that we can't fit into
the ABI the guest requires. This is a theoretical issue for many
syscalls, but a real issue for directory reads where the host
is using ext3 or ext4. There the 'offset' values retured via
the getdents syscall are hashes, and on a 64-bit system they
will always fill the full 64 bits.

Use the FD_32BIT_MODE fd flag to tell the kernel to stick
to 32-bit sized hashes for fds used by the guest.

This is an RFC patch because the kernel patch that adds the
new fd flag hasn't yet been accepted upstream. The kernel
patch is:
 https://patchew.org/QEMU/20200529072017.2906-1-linus.walleij@linaro.org/

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
This is just a minor update of the testing patch I sent out in the
thread discussing Linus's v1 kernel patch.

 linux-user/syscall.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 97de9fb5c92..265b9a096a0 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -884,6 +884,33 @@ static inline int host_to_target_sock_type(int host_type)
     return target_type;
 }
 
+/*
+ * If the guest is using a 32 bit ABI then we should try to ask the kernel
+ * to provide 32-bit offsets in getdents syscalls, as otherwise some
+ * filesystems will return 64-bit hash values which we can't fit into
+ * the field sizes the guest ABI mandates.
+ */
+#ifndef FD_32BIT_MODE
+#define FD_32BIT_MODE 2
+#endif
+
+static inline void request_32bit_fs(int fd)
+{
+#if HOST_LONG_BITS > TARGET_ABI_BITS
+    /*
+     * Ignore errors, which are likely due to the host kernel being
+     * too old to support FD_32BIT_MODE. We'll continue anyway, which
+     * might or might not work, depending on the guest code and on the
+     * host filesystem.
+     */
+    int flags = fcntl(fd, F_GETFD);
+    if (flags == -1) {
+        return;
+    }
+    fcntl(fd, F_SETFD, flags | FD_32BIT_MODE);
+#endif
+}
+
 static abi_ulong target_brk;
 static abi_ulong target_original_brk;
 static abi_ulong brk_page;
@@ -7725,6 +7752,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
                                   target_to_host_bitmask(arg2, fcntl_flags_tbl),
                                   arg3));
         fd_trans_unregister(ret);
+        request_32bit_fs(ret);
         unlock_user(p, arg1, 0);
         return ret;
 #endif
@@ -7735,6 +7763,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
                                   target_to_host_bitmask(arg3, fcntl_flags_tbl),
                                   arg4));
         fd_trans_unregister(ret);
+        request_32bit_fs(ret);
         unlock_user(p, arg2, 0);
         return ret;
 #if defined(TARGET_NR_name_to_handle_at) && defined(CONFIG_OPEN_BY_HANDLE)
@@ -7746,6 +7775,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
     case TARGET_NR_open_by_handle_at:
         ret = do_open_by_handle_at(arg1, arg2, arg3);
         fd_trans_unregister(ret);
+        request_32bit_fs(ret);
         return ret;
 #endif
     case TARGET_NR_close:
@@ -7790,6 +7820,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
             return -TARGET_EFAULT;
         ret = get_errno(creat(p, arg2));
         fd_trans_unregister(ret);
+        request_32bit_fs(ret);
         unlock_user(p, arg1, 0);
         return ret;
 #endif
@@ -12419,6 +12450,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
         }
         ret = get_errno(memfd_create(p, arg2));
         fd_trans_unregister(ret);
+        request_32bit_fs(ret);
         unlock_user(p, arg1, 0);
         return ret;
 #endif
-- 
2.20.1



^ permalink raw reply related	[flat|nested] 3+ messages in thread
* [PATCH 00/10] target/arm: Various v8.1M minor features
@ 2020-10-12 15:33 Peter Maydell
  2020-10-12 15:33 ` [RFC PATCH v2] linux-user: Use FD_32BIT_MODE fd flag for 32-bit guests Peter Maydell
  0 siblings, 1 reply; 3+ messages in thread
From: Peter Maydell @ 2020-10-12 15:33 UTC (permalink / raw)
  To: qemu-arm, qemu-devel; +Cc: Richard Henderson

This patchseries implements various minor v8.1M new features,
notably the branch-future and low-overhead-loop extensions.

(None of this will get enabled until we have enough to implement
a CPU model which has v8.1M, which will be the Cortex-M55, but
as usual we can get stuff into the tree gradually.)

Patch 1 is a decodetree fix suggested by Richard that is
necessary to avoid wrong-decode of the changes to t32.decode
by later patches.

thanks
-- PMM

Peter Maydell (10):
  decodetree: Fix codegen for non-overlapping group inside overlapping
    group
  target/arm: Implement v8.1M NOCP handling
  target/arm: Implement v8.1M conditional-select insns
  target/arm: Make the t32 insn[25:23]=111 group non-overlapping
  target/arm: Don't allow BLX imm for M-profile
  target/arm: Implement v8.1M branch-future insns (as NOPs)
  target/arm: Implement v8.1M low-overhead-loop instructions
  target/arm: Fix has_vfp/has_neon ID reg squashing for M-profile
  target/arm: Implement FPSCR.LTPSIZE for M-profile LOB extension
  target/arm: Fix writing to FPSCR.FZ16 on M-profile

 target/arm/cpu.h               |   7 ++
 target/arm/m-nocp.decode       |  10 ++-
 target/arm/t32.decode          |  50 +++++++----
 target/arm/cpu.c               |  34 ++++---
 target/arm/translate.c         | 157 +++++++++++++++++++++++++++++++++
 target/arm/vfp_helper.c        |  30 +++++--
 scripts/decodetree.py          |   2 +-
 target/arm/translate-vfp.c.inc |  17 +++-
 8 files changed, 268 insertions(+), 39 deletions(-)

-- 
2.20.1



^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-10-12 15:43 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
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2020-06-23 10:01 [RFC PATCH v2] linux-user: Use FD_32BIT_MODE fd flag for 32-bit guests Peter Maydell
2020-06-23 14:57 ` Laurent Vivier
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2020-10-12 15:33 [PATCH 00/10] target/arm: Various v8.1M minor features Peter Maydell
2020-10-12 15:33 ` [RFC PATCH v2] linux-user: Use FD_32BIT_MODE fd flag for 32-bit guests Peter Maydell

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