diff options

author	Alan Stern <stern@rowland.harvard.edu>	2016-05-19 16:29:50 -0400
committer	Greg Kroah-Hartman <gregkh@linuxfoundation.org>	2016-06-01 14:56:24 -0700
commit	85e3990bea49a50cb389015fea564b58899ab7c1 (patch)
tree	95e3543db5be9bd43fbe7e1808a717fd29d12fc1
parent	593224ea77b1ca842f45cf76f4deeef44dfbacd1 (diff)

USB: EHCI: avoid undefined pointer arithmetic and placate UBSAN

Several people have reported that UBSAN doesn't like the pointer arithmetic in ehci_hub_control(): u32 __iomem *status_reg = &ehci->regs->port_status[ (wIndex & 0xff) - 1]; u32 __iomem *hostpc_reg = &ehci->regs->hostpc[(wIndex & 0xff) - 1]; If wIndex is 0 (and it often is), these calculations underflow and UBSAN complains. According to the C standard, pointer computations leading to locations outside the bounds of an array object (other than 1 position past the end) are undefined. In this case, the compiler would be justified in concluding the wIndex can never be 0 and then optimizing away the tests for !wIndex that occur later in the subroutine. (Although, since ehci->regs->port_status and ehci->regs->hostpc are both 0-length arrays and are thus GCC extensions to the C standard, it's not clear what the compiler is really allowed to do.) At any rate, we can avoid all these difficulties, at the cost of making the code slightly longer, by not decrementing the index when it is equal to 0. The runtime effect is minimal, and anyway ehci_hub_control() is not on a hot path. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu> Reported-by: Meelis Roos <mroos@linux.ee> Reported-by: Martin_MOKREJÅ <mmokrejs@gmail.com> Reported-by: "Navin P.S" <navinp1912@gmail.com> CC: Andrey Ryabinin <ryabinin.a.a@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Diffstat


context:
space:
mode: