CVE-2022-49605

In the Linux kernel, the following vulnerability has been resolved:

igc: Reinstate IGC_REMOVED logic and implement it properly

The initially merged version of the igc driver code (via commit 146740f9abc4, "igc: Add support for PF") contained the following IGCREMOVED checks in the igcrd32/wr32() MMIO accessors:

u32 igc_rd32(struct igc_hw *hw, u32 reg)
{
    u8 __iomem *hw_addr = READ_ONCE(hw->hw_addr);
    u32 value = 0;

    if (IGC_REMOVED(hw_addr))
        return ~value;

    value = readl(&hw_addr[reg]);

    /* reads should not return all F's */
    if (!(~value) && (!reg || !(~readl(hw_addr))))
        hw->hw_addr = NULL;

    return value;
}

And:

#define wr32(reg, val) \
do { \
    u8 __iomem *hw_addr = READ_ONCE((hw)->hw_addr); \
    if (!IGC_REMOVED(hw_addr)) \
        writel((val), &hw_addr[(reg)]); \
} while (0)

E.g. igb has similar checks in its MMIO accessors, and has a similar macro E1000_REMOVED, which is implemented as follows:

#define E1000_REMOVED(h) unlikely(!(h))

These checks serve to detect and take note of an 0xffffffff MMIO read return from the device, which can be caused by a PCIe link flap or some other kind of PCI bus error, and to avoid performing MMIO reads and writes from that point onwards.

However, the IGC_REMOVED macro was not originally implemented:

#ifndef IGC_REMOVED
#define IGC_REMOVED(a) (0)
#endif /* IGC_REMOVED */

This led to the IGCREMOVED logic to be removed entirely in a subsequent commit (commit 3c215fb18e70, "igc: remove IGCREMOVED function"), with the rationale that such checks matter only for virtualization and that igc does not support virtualization -- but a PCIe device can become detached even without virtualization being in use, and without proper checks, a PCIe bus error affecting an igc adapter will lead to various NULL pointer dereferences, as the first access after the error will set hw->hw_addr to NULL, and subsequent accesses will blindly dereference this now-NULL pointer.

This patch reinstates the IGCREMOVED checks in igcrd32/wr32(), and implements IGCREMOVED the way it is done for igb, by checking for the unlikely() case of hwaddr being NULL. This change prevents the oopses seen when a PCIe link flap occurs on an igc adapter.