map: remove MapSpec.Freeze field #1558
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This has been an ambiguous flag since its inception. Internally, we would allow maps to be created with BPF_F_RDONLY_PROG, but not freeze them afterwards. Conversely, we would allow MapSpecs with Freeze set to 'true', but without the rdonly map flag set. The latter case has caused subtle bugs in the past, since BPF_MAP_FREEZE only blocks further modifications from user space, but doesn't actually mark the map as readonly for the verifier. This will prevent code pruning and other optimizations from taking place. This commit removes the Freeze field in favor of the map flag and adds a helper to keep existing call sites simple. Sourcegraph code search yields no references to this field in open-source code. Signed-off-by: Timo Beckers <[email protected]>
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In cilium#1558, it was pointed out that BPF_F_RDONLY_PROG only implies a map being read-only from bpf space, not user space. Using the flag to trigger freezing a map from user space doesn't make much sense. Change this to a name-based trigger, more closely resembling the libbpf behaviour. Signed-off-by: Timo Beckers <[email protected]>
ti-mo
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Sep 24, 2024
In #1558, it was pointed out that BPF_F_RDONLY_PROG only implies a map being read-only from bpf space, not user space. Using the flag to trigger freezing a map from user space doesn't make much sense. Change this to a name-based trigger, more closely resembling the libbpf behaviour. Signed-off-by: Timo Beckers <[email protected]>
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This has been an ambiguous flag since its inception. Internally, we would allow maps to be created with BPF_F_RDONLY_PROG, but not freeze them afterwards. Conversely, we would allow MapSpecs with Freeze set to 'true', but without the rdonly map flag set.
The latter case has caused subtle bugs in the past, since BPF_MAP_FREEZE only blocks further modifications from user space, but doesn't actually mark the map as readonly for the verifier. This will prevent code pruning and other optimizations from taking place.
This commit removes the Freeze field in favor of the map flag and adds a helper to keep existing call sites simple. Sourcegraph code search yields no references to this field in open-source code.