um: Discover host_task_size from envp

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When loading the UML binary, the host kernel will place the stack at the
highest possible address. It will then map the program name and
environment variables onto the start of the stack.

As such, an easy way to figure out the host_task_size is to use the
highest pointer to an environment variable as a reference.

Ensure that this works by disabling address layout randomization and
re-executing UML in case it was enabled.

This increases the available TASK_SIZE for 64 bit UML considerably.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20240919124511.282088-9-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

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Benjamin Berg 2024-09-19 14:45:09 +02:00 • committed by Johannes Berg

parent 830003c73d

commit 68b9883cc1

6 changed files with 29 additions and 159 deletions

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2

arch/um/include/shared/as-layout.h

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arch/um/include/shared/os.h

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21

arch/um/kernel/um_arch.c

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arch/um/os-Linux/main.c

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arch/x86/um/os-Linux/Makefile

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arch/x86/um/os-Linux/task_size.c

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