F4.7: endurecimiento de memoria — política W^X (exec-never) MPU#85
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…es MPU
- W^X: toda región MPU escribible se marca exec-never (bit XN del RASR), de modo
que ninguna región es a la vez escribible y ejecutable. El código vive SOLO en
flash (RX, write-never):
* SDRAM (heap): + XN
* KERNEL_RAM (data/bss/stacks): + XN
* APP_STACK (stack userland, app_region_for): + XN — userland no puede
ejecutar shellcode depositado en su propia pila.
(periféricos y stack-guard ya eran XN; flash es RX.)
- Auditoría de regiones MPU: nueva `mpu::audit_wx(&mut MPU)` que relee RASR de
las 8 regiones y verifica la invariante W^X (escribible ⇒ exec-never),
devolviendo bool. Reexportada como `mpu_audit_wx`. Defensa en profundidad:
detecta una regresión de atributos antes de exponer la superficie a userland.
- Ejemplos F407/F769: auditan W^X tras `platform_init` y lo registran
("W^X audit: PASS"). Detección de stack overflow ya cubierta por STACK_GUARD.
Validado RTT: F769 y F407 "W^X audit: PASS", todos los selftests PASS, kernel
estable, churn fault/respawn + safe-mode sin regresión (marcar la RAM exec-never
no rompe nada: el kernel ejecuta solo desde flash). host-tests 29 OK.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Resumen
mpu::audit_wx(reexportmpu_audit_wx) que relee RASR de las 8 regiones y verifica la invariante W^X en runtime; defensa en profundidad. Los ejemplos la registran al boot ("W^X audit: PASS").Validación
Test plan
🤖 Generated with Claude Code