* [PATCH] alpha/kernel/traps: Use find_vma_intersection() in traps for setting si_code
@ 2021-04-01 19:51 Liam Howlett
2021-04-01 20:25 ` Michel Lespinasse
0 siblings, 1 reply; 3+ messages in thread
From: Liam Howlett @ 2021-04-01 19:51 UTC (permalink / raw)
To: Richard Henderson, Ivan Kokshaysky, Matt Turner, Andrew Morton,
Liam Howlett, linux-alpha, linux-kernel
Cc: Dmitry Safonov, Michel Lespinasse, Gustavo A . R . Silva
find_vma() will continue to search upwards until the end of the virtual
memory space. This means the si_code would almost never be set to
SEGV_MAPERR even when the address falls outside of any VMA.
Using find_vma_intersection() allows for what is intended by only
returning a VMA if it falls within the range provided, in this case a
window of 1.
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
arch/alpha/kernel/traps.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c
index 921d4b6e4d95..7f51386c06d0 100644
--- a/arch/alpha/kernel/traps.c
+++ b/arch/alpha/kernel/traps.c
@@ -957,8 +957,10 @@ do_entUnaUser(void __user * va, unsigned long opcode,
si_code = SEGV_ACCERR;
else {
struct mm_struct *mm = current->mm;
+ unsigned long addr = (unsigned long)va;
+
mmap_read_lock(mm);
- if (find_vma(mm, (unsigned long)va))
+ if (find_vma_intersection(mm, addr, addr + 1))
si_code = SEGV_ACCERR;
else
si_code = SEGV_MAPERR;
--
2.30.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] alpha/kernel/traps: Use find_vma_intersection() in traps for setting si_code
2021-04-01 19:51 [PATCH] alpha/kernel/traps: Use find_vma_intersection() in traps for setting si_code Liam Howlett
@ 2021-04-01 20:25 ` Michel Lespinasse
2021-04-02 13:05 ` Liam Howlett
0 siblings, 1 reply; 3+ messages in thread
From: Michel Lespinasse @ 2021-04-01 20:25 UTC (permalink / raw)
To: Liam Howlett
Cc: Richard Henderson, Ivan Kokshaysky, Matt Turner, Andrew Morton,
linux-alpha, linux-kernel, Dmitry Safonov, Gustavo A . R . Silva
You are correct that find_vma is insufficient for what's intended
here, and that find_vma_intersection fixes it.
I'll let the arch maintainers speak of what the consequences of the
changed si_code would be - the bug has been here so long, that I would
worry some userspace might have come to depend on it (the old "common
law feature" issue).
Just a concern I have, with 0 evidence behind it, so I hope it turns
out not to be an actual issue.
Acked-by: Michel Lespinasse <walken@google.com>
On Thu, Apr 1, 2021 at 12:51 PM Liam Howlett <liam.howlett@oracle.com> wrote:
>
> find_vma() will continue to search upwards until the end of the virtual
> memory space. This means the si_code would almost never be set to
> SEGV_MAPERR even when the address falls outside of any VMA.
>
> Using find_vma_intersection() allows for what is intended by only
> returning a VMA if it falls within the range provided, in this case a
> window of 1.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> ---
> arch/alpha/kernel/traps.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c
> index 921d4b6e4d95..7f51386c06d0 100644
> --- a/arch/alpha/kernel/traps.c
> +++ b/arch/alpha/kernel/traps.c
> @@ -957,8 +957,10 @@ do_entUnaUser(void __user * va, unsigned long opcode,
> si_code = SEGV_ACCERR;
> else {
> struct mm_struct *mm = current->mm;
> + unsigned long addr = (unsigned long)va;
> +
> mmap_read_lock(mm);
> - if (find_vma(mm, (unsigned long)va))
> + if (find_vma_intersection(mm, addr, addr + 1))
> si_code = SEGV_ACCERR;
> else
> si_code = SEGV_MAPERR;
> --
> 2.30.0
--
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] alpha/kernel/traps: Use find_vma_intersection() in traps for setting si_code
2021-04-01 20:25 ` Michel Lespinasse
@ 2021-04-02 13:05 ` Liam Howlett
0 siblings, 0 replies; 3+ messages in thread
From: Liam Howlett @ 2021-04-02 13:05 UTC (permalink / raw)
To: Michel Lespinasse
Cc: Richard Henderson, Ivan Kokshaysky, Matt Turner, Andrew Morton,
linux-alpha, linux-kernel, Dmitry Safonov, Gustavo A . R . Silva
* Michel Lespinasse <walken@google.com> [210401 16:25]:
> You are correct that find_vma is insufficient for what's intended
> here, and that find_vma_intersection fixes it.
>
> I'll let the arch maintainers speak of what the consequences of the
> changed si_code would be - the bug has been here so long, that I would
> worry some userspace might have come to depend on it (the old "common
> law feature" issue).
Fair point. Is this a valid concern given the result will vary,
although uncommon, based on the address passed in? A user would see
different behaviour based on where the address lands in the virtual
address space.
> Just a concern I have, with 0 evidence behind it, so I hope it turns
> out not to be an actual issue.
>
> Acked-by: Michel Lespinasse <walken@google.com>
>
> On Thu, Apr 1, 2021 at 12:51 PM Liam Howlett <liam.howlett@oracle.com> wrote:
> >
> > find_vma() will continue to search upwards until the end of the virtual
> > memory space. This means the si_code would almost never be set to
> > SEGV_MAPERR even when the address falls outside of any VMA.
> >
> > Using find_vma_intersection() allows for what is intended by only
> > returning a VMA if it falls within the range provided, in this case a
> > window of 1.
> >
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> > ---
> > arch/alpha/kernel/traps.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c
> > index 921d4b6e4d95..7f51386c06d0 100644
> > --- a/arch/alpha/kernel/traps.c
> > +++ b/arch/alpha/kernel/traps.c
> > @@ -957,8 +957,10 @@ do_entUnaUser(void __user * va, unsigned long opcode,
> > si_code = SEGV_ACCERR;
> > else {
> > struct mm_struct *mm = current->mm;
> > + unsigned long addr = (unsigned long)va;
> > +
> > mmap_read_lock(mm);
> > - if (find_vma(mm, (unsigned long)va))
> > + if (find_vma_intersection(mm, addr, addr + 1))
> > si_code = SEGV_ACCERR;
> > else
> > si_code = SEGV_MAPERR;
> > --
> > 2.30.0
>
>
>
> --
> Michel "Walken" Lespinasse
> A program is never fully debugged until the last user dies.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-04-01 19:51 [PATCH] alpha/kernel/traps: Use find_vma_intersection() in traps for setting si_code Liam Howlett
2021-04-01 20:25 ` Michel Lespinasse
2021-04-02 13:05 ` Liam Howlett
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