| Message ID | 20210422105538.76057-1-ameynarkhede03@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Bjorn Helgaas |
| Headers | show |
| Series | [v2] PCI: Check value of resource alignment before using __ffs | expand |
On Thu, Apr 22, 2021 at 04:25:38PM +0530, Amey Narkhede wrote: > Return value of __ffs is undefined if no set bit exists in > its argument. This indicates that the associated BAR has > invalid alignment. > > Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com> > --- > drivers/pci/setup-bus.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > Thanks, Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
On 21/04/22 01:57PM, Leon Romanovsky wrote: > On Thu, Apr 22, 2021 at 04:25:38PM +0530, Amey Narkhede wrote: > > Return value of __ffs is undefined if no set bit exists in > > its argument. This indicates that the associated BAR has > > invalid alignment. > > > > Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com> > > --- > > drivers/pci/setup-bus.c | 9 +++++---- > > 1 file changed, 5 insertions(+), 4 deletions(-) > > > > Thanks, > Reviewed-by: Leon Romanovsky <leonro@nvidia.com> A gentle ping :)
On Thu, Apr 22, 2021 at 04:25:38PM +0530, Amey Narkhede wrote: > Return value of __ffs is undefined if no set bit exists in > its argument. This indicates that the associated BAR has > invalid alignment. > > Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com> > --- > drivers/pci/setup-bus.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c > index 2ce636937c6e..ce5380bdd2fd 100644 > --- a/drivers/pci/setup-bus.c > +++ b/drivers/pci/setup-bus.c > @@ -1044,10 +1044,11 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask, > * resources. > */ > align = pci_resource_alignment(dev, r); > - order = __ffs(align) - 20; > - if (order < 0) > - order = 0; > - if (order >= ARRAY_SIZE(aligns)) { > + if (align) { > + order = __ffs(align) - 20; > + order = (order < 0) ? 0 : order; > + } > + if (!align || order >= ARRAY_SIZE(aligns)) { > pci_warn(dev, "disabling BAR %d: %pR (bad alignment %#llx)\n", > i, r, (unsigned long long) align); > r->flags = 0; I know this is solving a theoretical problem. Is it also solving a *real* problem? I dislike the way it complicates the code and the usage of "align" and "order". I know that when "!align", we don't evaluate the "order >= ARRAY_SIZE()" (which would involve an uninitialized value), but it just seems ugly, and I'm not sure how much we benefit. And the "disabling BAR" part is gross. I know you're not changing that part, but it's just wrong. Setting r->flags = 0 certainly does not disable the BAR. It might make Linux ignore it, but that doesn't mean the hardware ignores it. When we turn on PCI_COMMAND_MEMORY, the BAR is enabled along with all the other memory BARs. Bjorn
On 21/05/25 05:01PM, Bjorn Helgaas wrote: > On Thu, Apr 22, 2021 at 04:25:38PM +0530, Amey Narkhede wrote: > > Return value of __ffs is undefined if no set bit exists in > > its argument. This indicates that the associated BAR has > > invalid alignment. > > > > Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com> > > --- > > drivers/pci/setup-bus.c | 9 +++++---- > > 1 file changed, 5 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c > > index 2ce636937c6e..ce5380bdd2fd 100644 > > --- a/drivers/pci/setup-bus.c > > +++ b/drivers/pci/setup-bus.c > > @@ -1044,10 +1044,11 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask, > > * resources. > > */ > > align = pci_resource_alignment(dev, r); > > - order = __ffs(align) - 20; > > - if (order < 0) > > - order = 0; > > - if (order >= ARRAY_SIZE(aligns)) { > > + if (align) { > > + order = __ffs(align) - 20; > > + order = (order < 0) ? 0 : order; > > + } > > + if (!align || order >= ARRAY_SIZE(aligns)) { > > pci_warn(dev, "disabling BAR %d: %pR (bad alignment %#llx)\n", > > i, r, (unsigned long long) align); > > r->flags = 0; > > I know this is solving a theoretical problem. Is it also solving a > *real* problem? > > I dislike the way it complicates the code and the usage of "align" and > "order". I know that when "!align", we don't evaluate the > "order >= ARRAY_SIZE()" (which would involve an uninitialized value), > but it just seems ugly, and I'm not sure how much we benefit. > > And the "disabling BAR" part is gross. I know you're not changing > that part, but it's just wrong. Setting r->flags = 0 certainly does > not disable the BAR. It might make Linux ignore it, but that doesn't > mean the hardware ignores it. When we turn on PCI_COMMAND_MEMORY, the > BAR is enabled along with all the other memory BARs. > > Bjorn Thanks for the detailed explanation. Is there any way to properly disable the BAR? On the side note do you think this problem is worth solving? I came across this during code inspection. I mean if practically there aren't chances of this bug occuring I'm okay with dropping this patch. Thanks, Amey
On Wed, May 26, 2021 at 02:36:12PM +0530, Amey Narkhede wrote: > On 21/05/25 05:01PM, Bjorn Helgaas wrote: > > On Thu, Apr 22, 2021 at 04:25:38PM +0530, Amey Narkhede wrote: > > > Return value of __ffs is undefined if no set bit exists in > > > its argument. This indicates that the associated BAR has > > > invalid alignment. > > > > > > Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com> > > > --- > > > drivers/pci/setup-bus.c | 9 +++++---- > > > 1 file changed, 5 insertions(+), 4 deletions(-) > > > > > > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c > > > index 2ce636937c6e..ce5380bdd2fd 100644 > > > --- a/drivers/pci/setup-bus.c > > > +++ b/drivers/pci/setup-bus.c > > > @@ -1044,10 +1044,11 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask, > > > * resources. > > > */ > > > align = pci_resource_alignment(dev, r); > > > - order = __ffs(align) - 20; > > > - if (order < 0) > > > - order = 0; > > > - if (order >= ARRAY_SIZE(aligns)) { > > > + if (align) { > > > + order = __ffs(align) - 20; > > > + order = (order < 0) ? 0 : order; > > > + } > > > + if (!align || order >= ARRAY_SIZE(aligns)) { > > > pci_warn(dev, "disabling BAR %d: %pR (bad alignment %#llx)\n", > > > i, r, (unsigned long long) align); > > > r->flags = 0; > > > > I know this is solving a theoretical problem. Is it also solving a > > *real* problem? > > > > I dislike the way it complicates the code and the usage of "align" and > > "order". I know that when "!align", we don't evaluate the > > "order >= ARRAY_SIZE()" (which would involve an uninitialized value), > > but it just seems ugly, and I'm not sure how much we benefit. > > > > And the "disabling BAR" part is gross. I know you're not changing > > that part, but it's just wrong. Setting r->flags = 0 certainly does > > not disable the BAR. It might make Linux ignore it, but that doesn't > > mean the hardware ignores it. When we turn on PCI_COMMAND_MEMORY, the > > BAR is enabled along with all the other memory BARs. > > > > Bjorn > > Thanks for the detailed explanation. Is there any way to properly > disable the BAR? Unfortunately there is no way to disable an individual BAR. PCI_COMMAND_MEMORY applied to *all* memory BARs, and the same for PCI_COMMAND_IO. > On the side note do you think this problem is > worth solving? I came across this during code inspection. > I mean if practically there aren't chances of > this bug occuring I'm okay with dropping this patch. I guess I would just drop it. Yes, it's a potential problem, but I couldn't figure out a solution that really seemed clean. Bjorn
diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c index 2ce636937c6e..ce5380bdd2fd 100644 --- a/drivers/pci/setup-bus.c +++ b/drivers/pci/setup-bus.c @@ -1044,10 +1044,11 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask, * resources. */ align = pci_resource_alignment(dev, r); - order = __ffs(align) - 20; - if (order < 0) - order = 0; - if (order >= ARRAY_SIZE(aligns)) { + if (align) { + order = __ffs(align) - 20; + order = (order < 0) ? 0 : order; + } + if (!align || order >= ARRAY_SIZE(aligns)) { pci_warn(dev, "disabling BAR %d: %pR (bad alignment %#llx)\n", i, r, (unsigned long long) align); r->flags = 0;
Return value of __ffs is undefined if no set bit exists in its argument. This indicates that the associated BAR has invalid alignment. Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com> --- drivers/pci/setup-bus.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) -- 2.31.1