diff options
| author | Johannes Berg <johannes.berg@intel.com> | 2025-04-04 17:05:19 +0200 |
|---|---|---|
| committer | Johannes Berg <johannes.berg@intel.com> | 2025-05-05 10:06:51 +0200 |
| commit | 68025adfc13e6cd15eebe2293f77659f47daf13b (patch) | |
| tree | ed250635fcbce5f1c21a12af1785d7e3891ec860 /arch/um/kernel | |
| parent | 92a09c47464d040866cf2b4cd052bc60555185fb (diff) | |
um: fix _nofault accesses
Nathan reported [1] that when built with clang, the um kernel
crashes pretty much immediately. This turned out to be an issue
with the inline assembly I had added, when clang used %rax/%eax
for both operands. Reorder it so current->thread.segv_continue
is written first, and then the lifetime of _faulted won't have
overlap with the lifetime of segv_continue.
In the email thread Benjamin also pointed out that current->mm
is only NULL for true kernel tasks, but we could do this for a
userspace task, so the current->thread.segv_continue logic must
be lifted out of the mm==NULL check.
Finally, while looking at this, put a barrier() so the NULL
assignment to thread.segv_continue cannot be reorder before
the possibly faulting operation.
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/r/20250402221254.GA384@ax162 [1]
Fixes: d1d7f01f7cd3 ("um: mark rodata read-only and implement _nofault accesses")
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Diffstat (limited to 'arch/um/kernel')
| -rw-r--r-- | arch/um/kernel/trap.c | 26 |
1 files changed, 13 insertions, 13 deletions
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c index ce073150dc20..ef2272e92a43 100644 --- a/arch/um/kernel/trap.c +++ b/arch/um/kernel/trap.c @@ -225,20 +225,20 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user, panic("Failed to sync kernel TLBs: %d", err); goto out; } - else if (current->mm == NULL) { - if (current->pagefault_disabled) { - if (!mc) { - show_regs(container_of(regs, struct pt_regs, regs)); - panic("Segfault with pagefaults disabled but no mcontext"); - } - if (!current->thread.segv_continue) { - show_regs(container_of(regs, struct pt_regs, regs)); - panic("Segfault without recovery target"); - } - mc_set_rip(mc, current->thread.segv_continue); - current->thread.segv_continue = NULL; - goto out; + else if (current->pagefault_disabled) { + if (!mc) { + show_regs(container_of(regs, struct pt_regs, regs)); + panic("Segfault with pagefaults disabled but no mcontext"); } + if (!current->thread.segv_continue) { + show_regs(container_of(regs, struct pt_regs, regs)); + panic("Segfault without recovery target"); + } + mc_set_rip(mc, current->thread.segv_continue); + current->thread.segv_continue = NULL; + goto out; + } + else if (current->mm == NULL) { show_regs(container_of(regs, struct pt_regs, regs)); panic("Segfault with no mm"); } |