SHADER VALIDATOR FOR VC4.(9)

💅 Shader validator for VC4.(9)

okay so bestie, this is a page from the Kernel API Manual — yes, the Kernel API Manual, we're literally in the big leagues now 🎀 — and it's all about the shader validator for VC4. sit down, hydrate, and let's get into it ✨

🌸 NAME 🌸

Shader validator for VC4. — the security bouncer standing between your shaders and the rest of system memory 🫶

💖 DESCRIPTION 💖

so here's the situation, and it's kind of a big deal 😭 the VC4 has no IOMMU between it and system memory. none. zero. not a single one 💀 which means if a user has access to execute shaders, they could legitimately escalate privilege — like, actual privilege escalation — by overwriting system memory (using the VPM write address register in the general-purpose DMA mode) or by reading system memory it shouldn't be reading (reading it as a texture, as uniform data, or via a direct-addressed TMU lookup). yeah. that's the whole vibe. not cute, but it's real 🙈

the shader validator walks over a shader's BO, making sure its accesses are appropriately bounded, and recording where texture accesses are made so that we can do relocations for them in the uniform stream. lowkey iconic bookkeeping behavior 👑

and here's the part where it gets chill: shader BO are immutable for their lifetimes — enforced by not allowing mmaps, GEM prime export, or rendering to from a CL 🌈 so this validation is only performed at BO creation time. one vibe check, at the door, and that's it. periodt 💅

bestie please remember: that immutability isn't a suggestion, it's enforced — the no-mmaps / no-GEM-prime-export / no-rendering-to-from-a-CL rules are literally what make validating once at BO creation time safe 🫶

🦋 SEE ALSO 🦋

• Kernel file ./drivers/gpu/drm/vc4/vc4_validate_shaders.c — go read the source, iykyk 📖

and that's the whole page, bestie 🎀 this masterpiece lives in ./drivers/gpu/drm/vc4 and it's dated October 2026 — slay, see you in the source tree, mwah 💖✨