[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen master] tools/ocaml/xc: Don't reference Abstract_Tag objects with the GC lock released
commit 9e7c74e6f9fd2e44df1212643b80af9032b45b07 Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> AuthorDate: Tue Jan 31 17:19:30 2023 +0000 Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CommitDate: Mon Feb 6 10:22:12 2023 +0000 tools/ocaml/xc: Don't reference Abstract_Tag objects with the GC lock released The intf->{addr,len} references in the xc_map_foreign_range() call are unsafe. From the manual: https://ocaml.org/manual/intfc.html#ss:parallel-execution-long-running-c-code "After caml_release_runtime_system() was called and until caml_acquire_runtime_system() is called, the C code must not access any OCaml data, nor call any function of the run-time system, nor call back into OCaml code." More than what the manual says, the intf pointer is (potentially) invalidated by caml_enter_blocking_section() if another thread happens to perform garbage collection at just the right (wrong) moment. Rewrite the logic. There's no need to stash data in the Ocaml object until the success path at the very end. Fixes: 8b7ce06a2d34 ("ocaml: Add XC bindings.") Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Acked-by: Christian Lindig <christian.lindig@xxxxxxxxxx> --- tools/ocaml/libs/xc/xenctrl_stubs.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) diff --git a/tools/ocaml/libs/xc/xenctrl_stubs.c b/tools/ocaml/libs/xc/xenctrl_stubs.c index 291663bb27..e5277f6f19 100644 --- a/tools/ocaml/libs/xc/xenctrl_stubs.c +++ b/tools/ocaml/libs/xc/xenctrl_stubs.c @@ -1028,26 +1028,25 @@ CAMLprim value stub_map_foreign_range(value xch, value dom, CAMLparam4(xch, dom, size, mfn); CAMLlocal1(result); struct mmap_interface *intf; - uint32_t c_dom; - unsigned long c_mfn; + unsigned long c_mfn = Nativeint_val(mfn); + int len = Int_val(size); + void *ptr; BUILD_BUG_ON((sizeof(struct mmap_interface) % sizeof(value)) != 0); result = caml_alloc(Wsize_bsize(sizeof(struct mmap_interface)), Abstract_tag); - intf = (struct mmap_interface *) result; - - intf->len = Int_val(size); - - c_dom = _D(dom); - c_mfn = Nativeint_val(mfn); caml_enter_blocking_section(); - intf->addr = xc_map_foreign_range(_H(xch), c_dom, - intf->len, PROT_READ|PROT_WRITE, - c_mfn); + ptr = xc_map_foreign_range(_H(xch), _D(dom), len, + PROT_READ|PROT_WRITE, c_mfn); caml_leave_blocking_section(); - if (!intf->addr) + + if (!ptr) caml_failwith("xc_map_foreign_range error"); + + intf = Data_abstract_val(result); + *intf = (struct mmap_interface){ ptr, len }; + CAMLreturn(result); } -- generated by git-patchbot for /home/xen/git/xen.git#master
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