Valgrind reports that statx arguments point to unaddressable bytes

[shepmaster]

I tried this code:

fn main() {
    std::fs::metadata("/").unwrap();
}

I compiled it and ran it under Valgrind:

$ rustc example.rs
$ valgrind ./example

I expected to see that Valgrind reported no errors.

Instead, it reports errors:

==1164== Memcheck, a memory error detector
==1164== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==1164== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==1164== Command: ./example
==1164==
==1164== Syscall param statx(file_name) points to unaddressable byte(s)
==1164==    at 0x49B094D: syscall (syscall.S:38)
==1164==    by 0x1149AB: statx (weak.rs:90)
==1164==    by 0x1149AB: std::sys::unix::fs::try_statx (fs.rs:132)
==1164==    by 0x11430E: std::sys::unix::fs::stat (fs.rs:995)
==1164==    by 0x10C43B: std::fs::metadata (in /home/ubuntu/example)
==1164==    by 0x10CBB2: example::main (in /home/ubuntu/example)
==1164==    by 0x10C382: std::rt::lang_start::{{closure}} (in /home/ubuntu/example)
==1164==    by 0x113082: {{closure}} (rt.rs:52)
==1164==    by 0x113082: std::panicking::try::do_call (panicking.rs:292)
==1164==    by 0x114E39: __rust_maybe_catch_panic (lib.rs:78)
==1164==    by 0x113A7F: try<i32,closure-0> (panicking.rs:270)
==1164==    by 0x113A7F: catch_unwind<closure-0,i32> (panic.rs:394)
==1164==    by 0x113A7F: std::rt::lang_start_internal (rt.rs:51)
==1164==    by 0x10C367: std::rt::lang_start (in /home/ubuntu/example)
==1164==    by 0x10CBEA: main (in /home/ubuntu/example)
==1164==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==1164==
==1164== Syscall param statx(buf) points to unaddressable byte(s)
==1164==    at 0x49B094D: syscall (syscall.S:38)
==1164==    by 0x1149AB: statx (weak.rs:90)
==1164==    by 0x1149AB: std::sys::unix::fs::try_statx (fs.rs:132)
==1164==    by 0x11430E: std::sys::unix::fs::stat (fs.rs:995)
==1164==    by 0x10C43B: std::fs::metadata (in /home/ubuntu/example)
==1164==    by 0x10CBB2: example::main (in /home/ubuntu/example)
==1164==    by 0x10C382: std::rt::lang_start::{{closure}} (in /home/ubuntu/example)
==1164==    by 0x113082: {{closure}} (rt.rs:52)
==1164==    by 0x113082: std::panicking::try::do_call (panicking.rs:292)
==1164==    by 0x114E39: __rust_maybe_catch_panic (lib.rs:78)
==1164==    by 0x113A7F: try<i32,closure-0> (panicking.rs:270)
==1164==    by 0x113A7F: catch_unwind<closure-0,i32> (panic.rs:394)
==1164==    by 0x113A7F: std::rt::lang_start_internal (rt.rs:51)
==1164==    by 0x10C367: std::rt::lang_start (in /home/ubuntu/example)
==1164==    by 0x10CBEA: main (in /home/ubuntu/example)
==1164==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

Meta

rustc --version --verbose:

$ rustc --version --verbose
rustc 1.41.0 (5e1a79984 2020-01-27)
binary: rustc
commit-hash: 5e1a799842ba6ed4a57e91f7ab9435947482f7d8
commit-date: 2020-01-27
host: x86_64-unknown-linux-gnu
release: 1.41.0
LLVM version: 9.0

rustc +nightly --version --verbose:

rustc 1.43.0-nightly (a29424a22 2020-02-07)
binary: rustc
commit-hash: a29424a2265411dda7d7446516ac5fd7499e2b55
commit-date: 2020-02-07
host: x86_64-unknown-linux-gnu
release: 1.43.0-nightly
LLVM version: 9.0

[shepmaster]

/cc @oxalica (from what appears to be the original commit)

[nagisa]

Looks genuine, we do indeed pass in 0s to the syscall:

statx(0, NULL, AT_STATX_SYNC_AS_STAT, STATX_ALL, NULL) = -1 EFAULT (Bad address)
statx(AT_FDCWD, "/", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_TYPE|STATX_MODE|STATX_NLINK|STATX_UID|STATX_GID|STATX_MTIME|STATX_CTIME|STATX_INO|STATX_SIZE|STATX_BLOCKS, stx_attributes=0, stx_mode=S_IFDIR|0755, stx_size=19, ...}) = 0

[glandium]

Try valgrind master. It was fixed there.

[nagisa]

@glandium what was? We do in fact get EFAULTed by the kernel, with or without valgrind.

[tmiasko]

https://sourceware.org/git/?p=valgrind.git;a=commit;h=2a7d3ae768f9e5b29acd5cb743c3fb13640a391c

[glandium]

As to why the "dubious" call: #65685

[nagisa]

Cool. Closing as inactionable.

[johan-bjareholt]

If anyone is wondering, the fix in valgrind is available on version 3.16.0 and up to be exact (released 2020-05-27).