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| author | Kees Cook <kees@kernel.org> | 2025-09-04 22:28:41 -0700 |
|---|---|---|
| committer | Kees Cook <kees@kernel.org> | 2025-09-08 14:58:20 -0700 |
| commit | 00e58ff924b3a684b076f9512fe2753be87b50e1 (patch) | |
| tree | 50acdda6a6e6a42394a6591055da4851ede6b71b | |
| parent | c17b750b3ad9f45f2b6f7e6f7f4679844244f0b9 (diff) | |
PCI: Test for bit underflow in pcie_set_readrq()
In preparation for the future commit ("bitops: Add __attribute_const__ to generic
ffs()-family implementations"), which allows GCC's value range tracker
to see past ffs(), GCC 8 on ARM thinks that it might be possible that
"ffs(rq) - 8" used here:
v = FIELD_PREP(PCI_EXP_DEVCTL_READRQ, ffs(rq) - 8);
could wrap below 0, leading to a very large value, which would be out of
range for the FIELD_PREP() usage:
drivers/pci/pci.c: In function 'pcie_set_readrq':
include/linux/compiler_types.h:572:38: error: call to '__compiletime_assert_471' declared with attribute error: FIELD_PREP: value too large for the field
...
drivers/pci/pci.c:5896:6: note: in expansion of macro 'FIELD_PREP'
v = FIELD_PREP(PCI_EXP_DEVCTL_READRQ, ffs(rq) - 8);
^~~~~~~~~~
If the result of the ffs() is bounds checked before being used in
FIELD_PREP(), the value tracker seems happy again. :)
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Closes: https://lore.kernel.org/linux-pci/CA+G9fYuysVr6qT8bjF6f08WLyCJRG7aXAeSd2F7=zTaHHd7L+Q@mail.gmail.com/
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250905052836.work.425-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
| -rw-r--r-- | drivers/pci/pci.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index b0f4d98036cd..005b92e6585e 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -5932,6 +5932,7 @@ int pcie_set_readrq(struct pci_dev *dev, int rq) { u16 v; int ret; + unsigned int firstbit; struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus); if (rq < 128 || rq > 4096 || !is_power_of_2(rq)) @@ -5949,7 +5950,10 @@ int pcie_set_readrq(struct pci_dev *dev, int rq) rq = mps; } - v = FIELD_PREP(PCI_EXP_DEVCTL_READRQ, ffs(rq) - 8); + firstbit = ffs(rq); + if (firstbit < 8) + return -EINVAL; + v = FIELD_PREP(PCI_EXP_DEVCTL_READRQ, firstbit - 8); if (bridge->no_inc_mrrs) { int max_mrrs = pcie_get_readrq(dev); |