After commit cbc654d18d37 ("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. :)
Fixes: cbc654d18d37 ("bitops: Add __attribute_const__ to generic ffs()-family implementations") Reported-by: Linux Kernel Functional Testing lkft@linaro.org Closes: https://lore.kernel.org/linux-pci/CA+G9fYuysVr6qT8bjF6f08WLyCJRG7aXAeSd2F7=z... Signed-off-by: Kees Cook kees@kernel.org --- Cc: Bjorn Helgaas bhelgaas@google.com Cc: Anders Roxell anders.roxell@linaro.org Cc: Naresh Kamboju naresh.kamboju@linaro.org Cc: lkft-triage@lists.linaro.org Cc: Linux Regressions regressions@lists.linux.dev Cc: Arnd Bergmann arnd@arndb.de Cc: Dan Carpenter dan.carpenter@linaro.org Cc: Ben Copeland benjamin.copeland@linaro.org Cc: lkft-triage@lists.linaro.org Cc: linux-pci@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- drivers/pci/pci.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
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);