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authorMark Rutland <mark.rutland@arm.com>2021-08-02 11:42:00 +0100
committerWill Deacon <will@kernel.org>2021-08-03 10:35:03 +0100
commite30e8d46cf605d216a799a28c77b8a41c328613a (patch)
treed44c5ba2d3cbbc1d021240be07a53dd4c2fa403c /certs
parentd8a719059b9dc963aa190598778ac804ff3e6a87 (diff)
arm64: fix compat syscall return truncation
Due to inconsistencies in the way we manipulate compat GPRs, we have a few issues today: * For audit and tracing, where error codes are handled as a (native) long, negative error codes are expected to be sign-extended to the native 64-bits, or they may fail to be matched correctly. Thus a syscall which fails with an error may erroneously be identified as failing. * For ptrace, *all* compat return values should be sign-extended for consistency with 32-bit arm, but we currently only do this for negative return codes. * As we may transiently set the upper 32 bits of some compat GPRs while in the kernel, these can be sampled by perf, which is somewhat confusing. This means that where a syscall returns a pointer above 2G, this will be sign-extended, but will not be mistaken for an error as error codes are constrained to the inclusive range [-4096, -1] where no user pointer can exist. To fix all of these, we must consistently use helpers to get/set the compat GPRs, ensuring that we never write the upper 32 bits of the return code, and always sign-extend when reading the return code. This patch does so, with the following changes: * We re-organise syscall_get_return_value() to always sign-extend for compat tasks, and reimplement syscall_get_error() atop. We update syscall_trace_exit() to use syscall_get_return_value(). * We consistently use syscall_set_return_value() to set the return value, ensureing the upper 32 bits are never set unexpectedly. * As the core audit code currently uses regs_return_value() rather than syscall_get_return_value(), we special-case this for compat_user_mode(regs) such that this will do the right thing. Going forward, we should try to move the core audit code over to syscall_get_return_value(). Cc: <stable@vger.kernel.org> Reported-by: He Zhe <zhe.he@windriver.com> Reported-by: weiyuchen <weiyuchen3@huawei.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Link: https://lore.kernel.org/r/20210802104200.21390-1-mark.rutland@arm.com Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'certs')
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