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bpf: add crosstask check to __bpf_get_stack #644

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danielocfb
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Pull request for series with
subject: bpf: add crosstask check to __bpf_get_stack
version: 2
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648

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Upstream branch: b4e59c1
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

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Upstream branch: b4e59c1
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from 2dc0f36 to 66ec86e Compare November 9, 2023 17:58
@danielocfb danielocfb force-pushed the bpf-next_base branch 2 times, most recently from 902178a to bc1b833 Compare November 9, 2023 18:41
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Upstream branch: 3815f89
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from 66ec86e to 1007cf8 Compare November 9, 2023 18:42
@danielocfb danielocfb force-pushed the bpf-next_base branch 2 times, most recently from 0fbe9f3 to b0d20d2 Compare November 9, 2023 19:02
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Upstream branch: 6f101db
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from 1007cf8 to 690904c Compare November 9, 2023 19:03
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Upstream branch: 6f101db
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from 690904c to 235d062 Compare November 9, 2023 19:13
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Upstream branch: e80742d
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from 235d062 to 9757c2d Compare November 9, 2023 19:21
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Upstream branch: e80742d
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from 9757c2d to 8debb67 Compare November 9, 2023 20:37
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Upstream branch: e80742d
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from 8debb67 to fc3a1c6 Compare November 9, 2023 21:00
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Upstream branch: e80742d
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from fc3a1c6 to b1352af Compare November 9, 2023 21:15
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Upstream branch: 155addf
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from b1352af to 4dc0483 Compare November 10, 2023 04:47
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Upstream branch: 689b097
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from 4dc0483 to 74aad25 Compare November 10, 2023 15:59
@jordalgo @d-e-s-o
bpf: add crosstask check to __bpf_get_stack
9903328 
Currently get_perf_callchain only supports user stack walking for
the current task. Passing the correct *crosstask* param will return
0 frames if the task passed to __bpf_get_stack isn't the current
one instead of a single incorrect frame/address. This change
passes the correct *crosstask* param but also does a preemptive
check in __bpf_get_stack if the task is current and returns
-EOPNOTSUPP if it is not.

This issue was found using bpf_get_task_stack inside a BPF
iterator ("iter/task"), which iterates over all tasks.
bpf_get_task_stack works fine for fetching kernel stacks
but because get_perf_callchain relies on the caller to know
if the requested *task* is the current one (via *crosstask*)
it was failing in a confusing way.

It might be possible to get user stacks for all tasks utilizing
something like access_process_vm but that requires the bpf
program calling bpf_get_task_stack to be sleepable and would
therefore be a breaking change.

Fixes: fa28dcb ("bpf: Introduce helper bpf_get_task_stack()")
Signed-off-by: Jordan Rome <[email protected]>
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Upstream branch: 9241176
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=799648
version: 2

@danielocfb danielocfb force-pushed the series/799648=>bpf-next branch from 74aad25 to 9903328 Compare November 10, 2023 17:08
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@danielocfb @jordalgo