Re: [PATCH] drm/panfrost: Prevent race when handling page fault
On 13/09/2019 18:24, Alyssa Rosenzweig wrote: I'm conflicted on this series. I'm on holiday, but thought I had to reply... On the one hand, userspace should obviously not be able to crash the kernel. So the crash should be fixed in one way or another. On the other hand, userspace really has to supply all the BOs it uses for correctness. I realize the DDK doesn't do this but... it probably should, umm... It turns out you don't need the missing BOs to trigger this - see the test case I added to IGT[1], referenced from v2 of this patch[2]. [1] https://patchwork.freedesktop.org/patch/330513/ [2] https://lore.kernel.org/lkml/20190913160310.50444-1-steven.pr...@arm.com/ Would it be possible to check for the NULL pointer in the kernel and skip printing information that would require a dereference? (Without having to play games with reference counts). Presumably that might fix crashes in other corner cases. I think we should try to do the right thing here and keep the reference counts correct. While it might be possible to handle the NULL pointer in practise the code has looked up the BO and is operating on it - so we should ensure that it can't disappear while that is happening. This isn't about supporting the quirks of the DDK - at the moment the DDK-on-Panfrost work I've been doing is really just a hack to be able to test the feasibility and it may yet never be published externally. But when I can trigger kernel bugs I might as well fix them! Steve On Thu, Sep 05, 2019 at 01:11:41PM +0100, Steven Price wrote: When handling a GPU page fault addr_to_drm_mm_node() is used to translate the GPU address to a buffer object. However it is possible for the buffer object to be freed after the function has returned resulting in a use-after-free of the BO. Change addr_to_drm_mm_node to return the panfrost_gem_object with an extra reference on it, preventing the BO from being freed until after the page fault has been handled. Signed-off-by: Steven Price --- I've managed to trigger this, generating the following stack trace. Unable to handle kernel NULL pointer dereference at virtual address 0090 pgd = 33a6a181 [0090] *pgd= Internal error: Oops: 5 [#1] SMP ARM Modules linked in: CPU: 0 PID: 81 Comm: irq/60-mmu Not tainted 5.3.0-rc1+ #4 Hardware name: Rockchip (Device Tree) PC is at panfrost_mmu_map_fault_addr+0x140/0x3a0 LR is at _raw_spin_unlock+0x20/0x3c pc : []lr : []psr: 20030013 sp : ec643e88 ip : ea70ce24 fp : ec5fe840 r10: 0001 r9 : r8 : 000178c9 r7 : r6 : 178c9f00 r5 : ec5fe940 r4 : ea70ce08 r3 : r2 : r1 : ec640e00 r0 : ec5fe940 Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none Control: 10c5387d Table: 29f8406a DAC: 0051 Process irq/60-mmu (pid: 81, stack limit = 0x4b907106) Stack: (0xec643e88 to 0xec644000) 3e80: ec640e00 c07cede0 c0c0b200 ec640e00 3ea0: 000178c9 c0c0b200 c07cede0 eef91040 ec5fe840 0001 3ec0: 00010001 010003c3 00c3 0001 178c9f00 c0508c98 eef91050 3ee0: ec643f34 c07c9188 0001 c0167854 ec643ef8 c0c08448 c07c933c 3f00: ec643f04 fffefffe 3d182b17 ee193468 ee193400 ec5db3c0 ec5db3c0 3f20: c0183840 ec5db3e4 c0cb2874 c0183b08 0001 c018385c e000 ee193400 3f40: ec5db3c0 c0183b8c c0c08448 6013 c01839b8 3d182b17 3f60: e000 ec5d0500 ec5db380 ec642000 ec5db3c0 c0183a64 ed025cd8 3f80: ec5d0538 c0146cfc ec642000 ec5db380 c0146bc0 3fa0: c01010b4 3fc0: 3fe0: 0013 [] (panfrost_mmu_map_fault_addr) from [] (panfrost_mmu_irq_handler_thread+0xf4/0x248) [] (panfrost_mmu_irq_handler_thread) from [] (irq_thread_fn+0x1c/0x58) [] (irq_thread_fn) from [] (irq_thread+0x128/0x240) [] (irq_thread) from [] (kthread+0x13c/0x154) [] (kthread) from [] (ret_from_fork+0x14/0x20) Exception stack(0xec643fb0 to 0xec643ff8) 3fa0: 3fc0: 3fe0: 0013 Code: 1aec eae8 e5143004 e59d2014 (e5933090) ---[ end trace 04eadc3009b8f507 ]--- --- drivers/gpu/drm/panfrost/panfrost_mmu.c | 38 - 1 file changed, 24 insertions(+), 14 deletions(-) diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c index 842bdd7cf6be..115925e7460a 100644 --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c @@ -392,9 +392,11 @@ void panfrost_mmu_pgtable_free(struct panfrost_file_priv *priv) free_io_pgtable_ops(mmu->pgtbl_ops); } -static struct drm_mm_node
Re: [PATCH] drm/panfrost: Prevent race when handling page fault
On Fri, Sep 13, 2019 at 01:24:54PM -0400, Alyssa Rosenzweig wrote: > I'm conflicted on this series. > > On the one hand, userspace should obviously not be able to crash the > kernel. So the crash should be fixed in one way or another. > > On the other hand, userspace really has to supply all the BOs it uses > for correctness. I realize the DDK doesn't do this but... it probably > should, umm... > > Would it be possible to check for the NULL pointer in the kernel and > skip printing information that would require a dereference? (Without > having to play games with reference counts). Presumably that might fix > crashes in other corner cases. Yeah if this is the blob doing something funny I guess the right action would be to kill that context and ban it from doing more funny things. So not just trying to bail out without crashing. Plus I guess the commit message should be a bit clearer in explaining what's actually going on here :-) -Daniel > > On Thu, Sep 05, 2019 at 01:11:41PM +0100, Steven Price wrote: > > When handling a GPU page fault addr_to_drm_mm_node() is used to > > translate the GPU address to a buffer object. However it is possible for > > the buffer object to be freed after the function has returned resulting > > in a use-after-free of the BO. > > > > Change addr_to_drm_mm_node to return the panfrost_gem_object with an > > extra reference on it, preventing the BO from being freed until after > > the page fault has been handled. > > > > Signed-off-by: Steven Price > > --- > > > > I've managed to trigger this, generating the following stack trace. > > > > Unable to handle kernel NULL pointer dereference at virtual address 0090 > > pgd = 33a6a181 > > [0090] *pgd= > > Internal error: Oops: 5 [#1] SMP ARM > > Modules linked in: > > CPU: 0 PID: 81 Comm: irq/60-mmu Not tainted 5.3.0-rc1+ #4 > > Hardware name: Rockchip (Device Tree) > > PC is at panfrost_mmu_map_fault_addr+0x140/0x3a0 > > LR is at _raw_spin_unlock+0x20/0x3c > > pc : []lr : []psr: 20030013 > > sp : ec643e88 ip : ea70ce24 fp : ec5fe840 > > r10: 0001 r9 : r8 : 000178c9 > > r7 : r6 : 178c9f00 r5 : ec5fe940 r4 : ea70ce08 > > r3 : r2 : r1 : ec640e00 r0 : ec5fe940 > > Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none > > Control: 10c5387d Table: 29f8406a DAC: 0051 > > Process irq/60-mmu (pid: 81, stack limit = 0x4b907106) > > Stack: (0xec643e88 to 0xec644000) > > 3e80: ec640e00 c07cede0 c0c0b200 ec640e00 > > > > 3ea0: 000178c9 c0c0b200 c07cede0 eef91040 ec5fe840 0001 > > > > 3ec0: 00010001 010003c3 00c3 0001 178c9f00 c0508c98 eef91050 > > > > 3ee0: ec643f34 c07c9188 0001 c0167854 ec643ef8 c0c08448 > > c07c933c > > 3f00: ec643f04 fffefffe 3d182b17 ee193468 ee193400 ec5db3c0 > > ec5db3c0 > > 3f20: c0183840 ec5db3e4 c0cb2874 c0183b08 0001 c018385c e000 > > ee193400 > > 3f40: ec5db3c0 c0183b8c c0c08448 6013 c01839b8 > > 3d182b17 > > 3f60: e000 ec5d0500 ec5db380 ec642000 ec5db3c0 c0183a64 > > ed025cd8 > > 3f80: ec5d0538 c0146cfc ec642000 ec5db380 c0146bc0 > > > > 3fa0: c01010b4 > > > > 3fc0: > > > > 3fe0: 0013 > > > > [] (panfrost_mmu_map_fault_addr) from [] > > (panfrost_mmu_irq_handler_thread+0xf4/0x248) > > [] (panfrost_mmu_irq_handler_thread) from [] > > (irq_thread_fn+0x1c/0x58) > > [] (irq_thread_fn) from [] (irq_thread+0x128/0x240) > > [] (irq_thread) from [] (kthread+0x13c/0x154) > > [] (kthread) from [] (ret_from_fork+0x14/0x20) > > Exception stack(0xec643fb0 to 0xec643ff8) > > 3fa0: > > > > 3fc0: > > > > 3fe0: 0013 > > Code: 1aec eae8 e5143004 e59d2014 (e5933090) > > ---[ end trace 04eadc3009b8f507 ]--- > > --- > > drivers/gpu/drm/panfrost/panfrost_mmu.c | 38 - > > 1 file changed, 24 insertions(+), 14 deletions(-) > > > > diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c > > b/drivers/gpu/drm/panfrost/panfrost_mmu.c > > index 842bdd7cf6be..115925e7460a 100644 > > --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c > > +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c > > @@ -392,9 +392,11 @@ void panfrost_mmu_pgtable_free(struct > > panfrost_file_priv *priv) > > free_io_pgtable_ops(mmu->pgtbl_ops); > > } > > > > -static struct drm_mm_node *addr_to_drm_mm_node(struct panfrost_device > > *pfdev, int as, u64 addr) > > +static struct panfrost_gem_object * > > +addr_to_drm_mm_node(struct panfrost_device *pfdev, int as, u64 addr) > >
Re: [PATCH] drm/panfrost: Prevent race when handling page fault
On Fri, Sep 13, 2019 at 12:25 PM Alyssa Rosenzweig
wrote:
>
> I'm conflicted on this series.
>
> On the one hand, userspace should obviously not be able to crash the
> kernel. So the crash should be fixed in one way or another.
>
> On the other hand, userspace really has to supply all the BOs it uses
> for correctness. I realize the DDK doesn't do this but... it probably
> should, umm...
>
> Would it be possible to check for the NULL pointer in the kernel and
> skip printing information that would require a dereference? (Without
> having to play games with reference counts). Presumably that might fix
> crashes in other corner cases.
I don't think that prevents the use after free. I think the NULL is a
pointer within the BO, not the BO. So we'd still be retrieving the
NULL ptr from a freed object.
Rob
>
> On Thu, Sep 05, 2019 at 01:11:41PM +0100, Steven Price wrote:
> > When handling a GPU page fault addr_to_drm_mm_node() is used to
> > translate the GPU address to a buffer object. However it is possible for
> > the buffer object to be freed after the function has returned resulting
> > in a use-after-free of the BO.
> >
> > Change addr_to_drm_mm_node to return the panfrost_gem_object with an
> > extra reference on it, preventing the BO from being freed until after
> > the page fault has been handled.
> >
> > Signed-off-by: Steven Price
> > ---
> >
> > I've managed to trigger this, generating the following stack trace.
> >
> > Unable to handle kernel NULL pointer dereference at virtual address 0090
> > pgd = 33a6a181
> > [0090] *pgd=
> > Internal error: Oops: 5 [#1] SMP ARM
> > Modules linked in:
> > CPU: 0 PID: 81 Comm: irq/60-mmu Not tainted 5.3.0-rc1+ #4
> > Hardware name: Rockchip (Device Tree)
> > PC is at panfrost_mmu_map_fault_addr+0x140/0x3a0
> > LR is at _raw_spin_unlock+0x20/0x3c
> > pc : []lr : []psr: 20030013
> > sp : ec643e88 ip : ea70ce24 fp : ec5fe840
> > r10: 0001 r9 : r8 : 000178c9
> > r7 : r6 : 178c9f00 r5 : ec5fe940 r4 : ea70ce08
> > r3 : r2 : r1 : ec640e00 r0 : ec5fe940
> > Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
> > Control: 10c5387d Table: 29f8406a DAC: 0051
> > Process irq/60-mmu (pid: 81, stack limit = 0x4b907106)
> > Stack: (0xec643e88 to 0xec644000)
> > 3e80: ec640e00 c07cede0 c0c0b200 ec640e00
> >
> > 3ea0: 000178c9 c0c0b200 c07cede0 eef91040 ec5fe840 0001
> >
> > 3ec0: 00010001 010003c3 00c3 0001 178c9f00 c0508c98 eef91050
> >
> > 3ee0: ec643f34 c07c9188 0001 c0167854 ec643ef8 c0c08448
> > c07c933c
> > 3f00: ec643f04 fffefffe 3d182b17 ee193468 ee193400 ec5db3c0
> > ec5db3c0
> > 3f20: c0183840 ec5db3e4 c0cb2874 c0183b08 0001 c018385c e000
> > ee193400
> > 3f40: ec5db3c0 c0183b8c c0c08448 6013 c01839b8
> > 3d182b17
> > 3f60: e000 ec5d0500 ec5db380 ec642000 ec5db3c0 c0183a64
> > ed025cd8
> > 3f80: ec5d0538 c0146cfc ec642000 ec5db380 c0146bc0
> >
> > 3fa0: c01010b4
> >
> > 3fc0:
> >
> > 3fe0: 0013
> >
> > [] (panfrost_mmu_map_fault_addr) from []
> > (panfrost_mmu_irq_handler_thread+0xf4/0x248)
> > [] (panfrost_mmu_irq_handler_thread) from []
> > (irq_thread_fn+0x1c/0x58)
> > [] (irq_thread_fn) from [] (irq_thread+0x128/0x240)
> > [] (irq_thread) from [] (kthread+0x13c/0x154)
> > [] (kthread) from [] (ret_from_fork+0x14/0x20)
> > Exception stack(0xec643fb0 to 0xec643ff8)
> > 3fa0:
> >
> > 3fc0:
> >
> > 3fe0: 0013
> > Code: 1aec eae8 e5143004 e59d2014 (e5933090)
> > ---[ end trace 04eadc3009b8f507 ]---
> > ---
> > drivers/gpu/drm/panfrost/panfrost_mmu.c | 38 -
> > 1 file changed, 24 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> > b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> > index 842bdd7cf6be..115925e7460a 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> > @@ -392,9 +392,11 @@ void panfrost_mmu_pgtable_free(struct
> > panfrost_file_priv *priv)
> > free_io_pgtable_ops(mmu->pgtbl_ops);
> > }
> >
> > -static struct drm_mm_node *addr_to_drm_mm_node(struct panfrost_device
> > *pfdev, int as, u64 addr)
> > +static struct panfrost_gem_object *
> > +addr_to_drm_mm_node(struct panfrost_device *pfdev, int as, u64 addr)
> > {
> > - struct drm_mm_node *node = NULL;
> > + struct panfrost_gem_object *bo = NULL;
> > + struct drm_mm_node *node;
> > u64
Re: [PATCH] drm/panfrost: Prevent race when handling page fault
I'm conflicted on this series.
On the one hand, userspace should obviously not be able to crash the
kernel. So the crash should be fixed in one way or another.
On the other hand, userspace really has to supply all the BOs it uses
for correctness. I realize the DDK doesn't do this but... it probably
should, umm...
Would it be possible to check for the NULL pointer in the kernel and
skip printing information that would require a dereference? (Without
having to play games with reference counts). Presumably that might fix
crashes in other corner cases.
On Thu, Sep 05, 2019 at 01:11:41PM +0100, Steven Price wrote:
> When handling a GPU page fault addr_to_drm_mm_node() is used to
> translate the GPU address to a buffer object. However it is possible for
> the buffer object to be freed after the function has returned resulting
> in a use-after-free of the BO.
>
> Change addr_to_drm_mm_node to return the panfrost_gem_object with an
> extra reference on it, preventing the BO from being freed until after
> the page fault has been handled.
>
> Signed-off-by: Steven Price
> ---
>
> I've managed to trigger this, generating the following stack trace.
>
> Unable to handle kernel NULL pointer dereference at virtual address 0090
> pgd = 33a6a181
> [0090] *pgd=
> Internal error: Oops: 5 [#1] SMP ARM
> Modules linked in:
> CPU: 0 PID: 81 Comm: irq/60-mmu Not tainted 5.3.0-rc1+ #4
> Hardware name: Rockchip (Device Tree)
> PC is at panfrost_mmu_map_fault_addr+0x140/0x3a0
> LR is at _raw_spin_unlock+0x20/0x3c
> pc : []lr : []psr: 20030013
> sp : ec643e88 ip : ea70ce24 fp : ec5fe840
> r10: 0001 r9 : r8 : 000178c9
> r7 : r6 : 178c9f00 r5 : ec5fe940 r4 : ea70ce08
> r3 : r2 : r1 : ec640e00 r0 : ec5fe940
> Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
> Control: 10c5387d Table: 29f8406a DAC: 0051
> Process irq/60-mmu (pid: 81, stack limit = 0x4b907106)
> Stack: (0xec643e88 to 0xec644000)
> 3e80: ec640e00 c07cede0 c0c0b200 ec640e00
> 3ea0: 000178c9 c0c0b200 c07cede0 eef91040 ec5fe840 0001
> 3ec0: 00010001 010003c3 00c3 0001 178c9f00 c0508c98 eef91050
> 3ee0: ec643f34 c07c9188 0001 c0167854 ec643ef8 c0c08448 c07c933c
> 3f00: ec643f04 fffefffe 3d182b17 ee193468 ee193400 ec5db3c0 ec5db3c0
> 3f20: c0183840 ec5db3e4 c0cb2874 c0183b08 0001 c018385c e000 ee193400
> 3f40: ec5db3c0 c0183b8c c0c08448 6013 c01839b8 3d182b17
> 3f60: e000 ec5d0500 ec5db380 ec642000 ec5db3c0 c0183a64 ed025cd8
> 3f80: ec5d0538 c0146cfc ec642000 ec5db380 c0146bc0
> 3fa0: c01010b4
> 3fc0:
> 3fe0: 0013
> [] (panfrost_mmu_map_fault_addr) from []
> (panfrost_mmu_irq_handler_thread+0xf4/0x248)
> [] (panfrost_mmu_irq_handler_thread) from []
> (irq_thread_fn+0x1c/0x58)
> [] (irq_thread_fn) from [] (irq_thread+0x128/0x240)
> [] (irq_thread) from [] (kthread+0x13c/0x154)
> [] (kthread) from [] (ret_from_fork+0x14/0x20)
> Exception stack(0xec643fb0 to 0xec643ff8)
> 3fa0:
> 3fc0:
> 3fe0: 0013
> Code: 1aec eae8 e5143004 e59d2014 (e5933090)
> ---[ end trace 04eadc3009b8f507 ]---
> ---
> drivers/gpu/drm/panfrost/panfrost_mmu.c | 38 -
> 1 file changed, 24 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index 842bdd7cf6be..115925e7460a 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -392,9 +392,11 @@ void panfrost_mmu_pgtable_free(struct panfrost_file_priv
> *priv)
> free_io_pgtable_ops(mmu->pgtbl_ops);
> }
>
> -static struct drm_mm_node *addr_to_drm_mm_node(struct panfrost_device
> *pfdev, int as, u64 addr)
> +static struct panfrost_gem_object *
> +addr_to_drm_mm_node(struct panfrost_device *pfdev, int as, u64 addr)
> {
> - struct drm_mm_node *node = NULL;
> + struct panfrost_gem_object *bo = NULL;
> + struct drm_mm_node *node;
> u64 offset = addr >> PAGE_SHIFT;
> struct panfrost_mmu *mmu;
>
> @@ -406,14 +408,17 @@ static struct drm_mm_node *addr_to_drm_mm_node(struct
> panfrost_device *pfdev, in
>
> priv = container_of(mmu, struct panfrost_file_priv, mmu);
> drm_mm_for_each_node(node, >mm) {
> - if (offset >= node->start && offset < (node->start +
> node->size))
> + if (offset >= node->start &&
> + offset <
Re: [PATCH] drm/panfrost: Prevent race when handling page fault
On 07/09/2019 20:36, Daniel Vetter wrote: > On Fri, Sep 6, 2019 at 2:42 PM Steven Price wrote: >> >> On 06/09/2019 12:10, Rob Herring wrote: >>> On Thu, Sep 5, 2019 at 1:11 PM Steven Price wrote: When handling a GPU page fault addr_to_drm_mm_node() is used to translate the GPU address to a buffer object. However it is possible for the buffer object to be freed after the function has returned resulting in a use-after-free of the BO. Change addr_to_drm_mm_node to return the panfrost_gem_object with an extra reference on it, preventing the BO from being freed until after the page fault has been handled. Signed-off-by: Steven Price --- I've managed to trigger this, generating the following stack trace. >>> >>> Humm, the assumption was that a fault could only happen during a job >>> and so a reference would already be held. Otherwise, couldn't the GPU >>> also be accessing the BO after it is freed? >> >> Ah, I guess I missed that in the commit message. This is assuming that >> user space doesn't include the BO in the job even though the GPU then >> does try to access it. AIUI mesa wouldn't do this, but this is still >> easily possible if user space wants to crash the kernel. > > Do we have some nice regression tests for uapi exploits and corner > cases like this? Maybe even in igt? > -Daniel Not currently, I've been playing with the idea of getting the closed-source DDK blob running on Panfrost and this is what generates the "not-quite-mesa" usage. It would definitely be good extend the test cases in IGT, I have a synthetic test which can trigger this - I just need to get approval to post it. Steve ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
Re: [PATCH] drm/panfrost: Prevent race when handling page fault
On Fri, Sep 6, 2019 at 2:42 PM Steven Price wrote:
>
> On 06/09/2019 12:10, Rob Herring wrote:
> > On Thu, Sep 5, 2019 at 1:11 PM Steven Price wrote:
> >>
> >> When handling a GPU page fault addr_to_drm_mm_node() is used to
> >> translate the GPU address to a buffer object. However it is possible for
> >> the buffer object to be freed after the function has returned resulting
> >> in a use-after-free of the BO.
> >>
> >> Change addr_to_drm_mm_node to return the panfrost_gem_object with an
> >> extra reference on it, preventing the BO from being freed until after
> >> the page fault has been handled.
> >>
> >> Signed-off-by: Steven Price
> >> ---
> >>
> >> I've managed to trigger this, generating the following stack trace.
> >
> > Humm, the assumption was that a fault could only happen during a job
> > and so a reference would already be held. Otherwise, couldn't the GPU
> > also be accessing the BO after it is freed?
>
> Ah, I guess I missed that in the commit message. This is assuming that
> user space doesn't include the BO in the job even though the GPU then
> does try to access it. AIUI mesa wouldn't do this, but this is still
> easily possible if user space wants to crash the kernel.
Do we have some nice regression tests for uapi exploits and corner
cases like this? Maybe even in igt?
-Daniel
>
> > Also, looking at this again, I think we need to hold the mm_lock
> > around the drm_mm_for_each_node().
>
> Ah, good point. Squashing in the following should do the trick:
>
> 8<
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index ccc536d2e489..41f297aa259c 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -396,26 +396,33 @@ static struct panfrost_gem_object *
> addr_to_drm_mm_node(struct panfrost_device *pfdev, int as, u64 addr)
> {
> struct panfrost_gem_object *bo = NULL;
> + struct panfrost_file_priv *priv;
> struct drm_mm_node *node;
> u64 offset = addr >> PAGE_SHIFT;
> struct panfrost_mmu *mmu;
>
> spin_lock(>as_lock);
> list_for_each_entry(mmu, >as_lru_list, list) {
> - struct panfrost_file_priv *priv;
> - if (as != mmu->as)
> - continue;
> + if (as == mmu->as)
> + break;
> + }
> + if (as != mmu->as)
> + goto out;
>
> - priv = container_of(mmu, struct panfrost_file_priv, mmu);
> - drm_mm_for_each_node(node, >mm) {
> - if (offset >= node->start &&
> - offset < (node->start + node->size)) {
> - bo = drm_mm_node_to_panfrost_bo(node);
> - drm_gem_object_get(>base.base);
> - goto out;
> - }
> + priv = container_of(mmu, struct panfrost_file_priv, mmu);
> +
> + spin_lock(>mm_lock);
> +
> + drm_mm_for_each_node(node, >mm) {
> + if (offset >= node->start &&
> + offset < (node->start + node->size)) {
> + bo = drm_mm_node_to_panfrost_bo(node);
> + drm_gem_object_get(>base.base);
> + break;
> }
> }
> +
> + spin_unlock(>mm_lock);
> out:
> spin_unlock(>as_lock);
> return bo;
> ___
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
Re: [PATCH] drm/panfrost: Prevent race when handling page fault
On 06/09/2019 12:10, Rob Herring wrote:
> On Thu, Sep 5, 2019 at 1:11 PM Steven Price wrote:
>>
>> When handling a GPU page fault addr_to_drm_mm_node() is used to
>> translate the GPU address to a buffer object. However it is possible for
>> the buffer object to be freed after the function has returned resulting
>> in a use-after-free of the BO.
>>
>> Change addr_to_drm_mm_node to return the panfrost_gem_object with an
>> extra reference on it, preventing the BO from being freed until after
>> the page fault has been handled.
>>
>> Signed-off-by: Steven Price
>> ---
>>
>> I've managed to trigger this, generating the following stack trace.
>
> Humm, the assumption was that a fault could only happen during a job
> and so a reference would already be held. Otherwise, couldn't the GPU
> also be accessing the BO after it is freed?
Ah, I guess I missed that in the commit message. This is assuming that
user space doesn't include the BO in the job even though the GPU then
does try to access it. AIUI mesa wouldn't do this, but this is still
easily possible if user space wants to crash the kernel.
> Also, looking at this again, I think we need to hold the mm_lock
> around the drm_mm_for_each_node().
Ah, good point. Squashing in the following should do the trick:
8<
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c
b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index ccc536d2e489..41f297aa259c 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -396,26 +396,33 @@ static struct panfrost_gem_object *
addr_to_drm_mm_node(struct panfrost_device *pfdev, int as, u64 addr)
{
struct panfrost_gem_object *bo = NULL;
+ struct panfrost_file_priv *priv;
struct drm_mm_node *node;
u64 offset = addr >> PAGE_SHIFT;
struct panfrost_mmu *mmu;
spin_lock(>as_lock);
list_for_each_entry(mmu, >as_lru_list, list) {
- struct panfrost_file_priv *priv;
- if (as != mmu->as)
- continue;
+ if (as == mmu->as)
+ break;
+ }
+ if (as != mmu->as)
+ goto out;
- priv = container_of(mmu, struct panfrost_file_priv, mmu);
- drm_mm_for_each_node(node, >mm) {
- if (offset >= node->start &&
- offset < (node->start + node->size)) {
- bo = drm_mm_node_to_panfrost_bo(node);
- drm_gem_object_get(>base.base);
- goto out;
- }
+ priv = container_of(mmu, struct panfrost_file_priv, mmu);
+
+ spin_lock(>mm_lock);
+
+ drm_mm_for_each_node(node, >mm) {
+ if (offset >= node->start &&
+ offset < (node->start + node->size)) {
+ bo = drm_mm_node_to_panfrost_bo(node);
+ drm_gem_object_get(>base.base);
+ break;
}
}
+
+ spin_unlock(>mm_lock);
out:
spin_unlock(>as_lock);
return bo;
Re: [PATCH] drm/panfrost: Prevent race when handling page fault
On Thu, Sep 5, 2019 at 1:11 PM Steven Price wrote: > > When handling a GPU page fault addr_to_drm_mm_node() is used to > translate the GPU address to a buffer object. However it is possible for > the buffer object to be freed after the function has returned resulting > in a use-after-free of the BO. > > Change addr_to_drm_mm_node to return the panfrost_gem_object with an > extra reference on it, preventing the BO from being freed until after > the page fault has been handled. > > Signed-off-by: Steven Price > --- > > I've managed to trigger this, generating the following stack trace. Humm, the assumption was that a fault could only happen during a job and so a reference would already be held. Otherwise, couldn't the GPU also be accessing the BO after it is freed? Also, looking at this again, I think we need to hold the mm_lock around the drm_mm_for_each_node(). Rob ___ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
[PATCH] drm/panfrost: Prevent race when handling page fault
When handling a GPU page fault addr_to_drm_mm_node() is used to
translate the GPU address to a buffer object. However it is possible for
the buffer object to be freed after the function has returned resulting
in a use-after-free of the BO.
Change addr_to_drm_mm_node to return the panfrost_gem_object with an
extra reference on it, preventing the BO from being freed until after
the page fault has been handled.
Signed-off-by: Steven Price
---
I've managed to trigger this, generating the following stack trace.
Unable to handle kernel NULL pointer dereference at virtual address 0090
pgd = 33a6a181
[0090] *pgd=
Internal error: Oops: 5 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 81 Comm: irq/60-mmu Not tainted 5.3.0-rc1+ #4
Hardware name: Rockchip (Device Tree)
PC is at panfrost_mmu_map_fault_addr+0x140/0x3a0
LR is at _raw_spin_unlock+0x20/0x3c
pc : []lr : []psr: 20030013
sp : ec643e88 ip : ea70ce24 fp : ec5fe840
r10: 0001 r9 : r8 : 000178c9
r7 : r6 : 178c9f00 r5 : ec5fe940 r4 : ea70ce08
r3 : r2 : r1 : ec640e00 r0 : ec5fe940
Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
Control: 10c5387d Table: 29f8406a DAC: 0051
Process irq/60-mmu (pid: 81, stack limit = 0x4b907106)
Stack: (0xec643e88 to 0xec644000)
3e80: ec640e00 c07cede0 c0c0b200 ec640e00
3ea0: 000178c9 c0c0b200 c07cede0 eef91040 ec5fe840 0001
3ec0: 00010001 010003c3 00c3 0001 178c9f00 c0508c98 eef91050
3ee0: ec643f34 c07c9188 0001 c0167854 ec643ef8 c0c08448 c07c933c
3f00: ec643f04 fffefffe 3d182b17 ee193468 ee193400 ec5db3c0 ec5db3c0
3f20: c0183840 ec5db3e4 c0cb2874 c0183b08 0001 c018385c e000 ee193400
3f40: ec5db3c0 c0183b8c c0c08448 6013 c01839b8 3d182b17
3f60: e000 ec5d0500 ec5db380 ec642000 ec5db3c0 c0183a64 ed025cd8
3f80: ec5d0538 c0146cfc ec642000 ec5db380 c0146bc0
3fa0: c01010b4
3fc0:
3fe0: 0013
[] (panfrost_mmu_map_fault_addr) from []
(panfrost_mmu_irq_handler_thread+0xf4/0x248)
[] (panfrost_mmu_irq_handler_thread) from []
(irq_thread_fn+0x1c/0x58)
[] (irq_thread_fn) from [] (irq_thread+0x128/0x240)
[] (irq_thread) from [] (kthread+0x13c/0x154)
[] (kthread) from [] (ret_from_fork+0x14/0x20)
Exception stack(0xec643fb0 to 0xec643ff8)
3fa0:
3fc0:
3fe0: 0013
Code: 1aec eae8 e5143004 e59d2014 (e5933090)
---[ end trace 04eadc3009b8f507 ]---
---
drivers/gpu/drm/panfrost/panfrost_mmu.c | 38 -
1 file changed, 24 insertions(+), 14 deletions(-)
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c
b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index 842bdd7cf6be..115925e7460a 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -392,9 +392,11 @@ void panfrost_mmu_pgtable_free(struct panfrost_file_priv
*priv)
free_io_pgtable_ops(mmu->pgtbl_ops);
}
-static struct drm_mm_node *addr_to_drm_mm_node(struct panfrost_device *pfdev,
int as, u64 addr)
+static struct panfrost_gem_object *
+addr_to_drm_mm_node(struct panfrost_device *pfdev, int as, u64 addr)
{
- struct drm_mm_node *node = NULL;
+ struct panfrost_gem_object *bo = NULL;
+ struct drm_mm_node *node;
u64 offset = addr >> PAGE_SHIFT;
struct panfrost_mmu *mmu;
@@ -406,14 +408,17 @@ static struct drm_mm_node *addr_to_drm_mm_node(struct
panfrost_device *pfdev, in
priv = container_of(mmu, struct panfrost_file_priv, mmu);
drm_mm_for_each_node(node, >mm) {
- if (offset >= node->start && offset < (node->start +
node->size))
+ if (offset >= node->start &&
+ offset < (node->start + node->size)) {
+ bo = drm_mm_node_to_panfrost_bo(node);
+ drm_gem_object_get(>base.base);
goto out;
+ }
}
}
-
out:
spin_unlock(>as_lock);
- return node;
+ return bo;
}
#define NUM_FAULT_PAGES (SZ_2M / PAGE_SIZE)
@@ -421,29 +426,28 @@ static struct drm_mm_node *addr_to_drm_mm_node(struct
panfrost_device *pfdev, in
int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as, u64
addr)
{
int ret, i;
- struct drm_mm_node *node;
struct panfrost_gem_object *bo;
struct address_space *mapping;
pgoff_t page_offset;
struct sg_table *sgt;
