tools/debug: add read-only GMMU/pdb scanners for live guest RAM

pdb_scan_gmmu walks the GP10X/VER2 GMMU page-table format (PD3/PD2/PD1/
PD0/PT, 16-byte dual PD0 entries, sys/vidmem apertures) and pdb_scan is
the x86-64 index cross-check.  Both map the QEMU pc.ram file correctly
for the 2 GiB low + high-RAM q35 layout and are strictly read-only.
Used to prove the ring page/VA and pdb chains in CONT.435/436.

1 files changed, 234 insertions, 0 deletions

diff --git a/tools/debug/pdb_scan.c b/tools/debug/pdb_scan.c
new file mode 100644
index 0000000..da7227e
--- /dev/null
+++ b/tools/debug/pdb_scan.c
@@ -0,0 +1,234 @@
+/*
+ * pdb_scan.c - read-only reverse scan of a QEMU pc.ram backing file for the
+ * 4-level page-table chain that maps a given VA to a given PA.
+ *
+ * Build:
+ *   cc -O2 -Wall -Wextra -o pdb_scan pdb_scan.c
+ *
+ * Usage:
+ *   sudo ./pdb_scan /dev/shm/vgpu-guest-ram 0xafef8000 0x4100000
+ *
+ * Arguments: <ramfile> <target_pa> [va]
+ *   - target_pa : physical address the leaf PT entry must point at (page aligned)
+ *   - va        : optional VA used to derive the four table indices
+ *                 (default 0x4100000: PML4[0], PDPT[0], PD[8], PT[0x100])
+ *
+ * The scan is strictly read-only: the file is mmap()ed PROT_READ/MAP_PRIVATE
+ * and no writes are issued.  It builds two reverse indexes:
+ *   entry[0x000] -> pages (used for PML4[0] and PDPT[0])
+ *   entry[0x040] -> pages (used for PD[8])
+ * then joins them against pages whose entry[0x800] points at target_pa.
+ */
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+
+#define PAGE_SHIFT 12ULL
+#define PAGE_SIZE  (1ULL << PAGE_SHIFT)
+#define PA_MASK    0x000FFFFFFFFFF000ULL
+
+static uint64_t target_pa;
+static uint64_t va;
+static uint64_t n_pages;
+static const uint8_t *ram;
+
+static unsigned idx_pml4, idx_pdpt, idx_pd, idx_pt;
+static const char *idx_names[4] = {"PML4", "PDPT", "PD", "PT"};
+
+static inline uint64_t rd64(uint64_t pa)
+{
+    uint64_t v;
+    memcpy(&v, ram + pa, sizeof(v));
+    return v;
+}
+
+static inline uint64_t entry_mask(uint64_t e) { return e & PA_MASK; }
+
+static const char *bits(uint64_t e)
+{
+    static char b[128];
+    snprintf(b, sizeof(b), "P=%d RW=%d US=%d PWT=%d PCD=%d A=%d D=%d PS=%d",
+             (int)(e & 1), (int)((e >> 1) & 1), (int)((e >> 2) & 1),
+             (int)((e >> 3) & 1), (int)((e >> 4) & 1), (int)((e >> 5) & 1),
+             (int)((e >> 6) & 1), (int)((e >> 7) & 1));
+    return b;
+}
+
+/* Generic 4-level walk; returns final PA (masked) or UINT64_MAX on break. */
+static uint64_t walk4(uint64_t pml4_pa, uint64_t *raw_out)
+{
+    uint64_t e[4], pa = pml4_pa;
+    unsigned idx[4] = {idx_pml4, idx_pdpt, idx_pd, idx_pt};
+    int l;
+    for (l = 0; l < 4; l++) {
+        if (pa + PAGE_SIZE > (n_pages << PAGE_SHIFT))
+            return UINT64_MAX;
+        e[l] = rd64(pa + (uint64_t)idx[l] * 8);
+        if (raw_out) raw_out[l] = e[l];
+        if (!(e[l] & 1))
+            return UINT64_MAX;
+        if (l == 2 && (e[l] & 0x80)) { /* PS=1: 2 MiB page at PD level */
+            uint64_t base = entry_mask(e[l]) & ~((1ULL << 21) - 1);
+            return base | (va & ((1ULL << 21) - 1));
+        }
+        pa = entry_mask(e[l]);
+    }
+    return pa;
+}
+
+int main(int argc, char **argv)
+{
+    const char *path;
+    int fd;
+    struct stat st;
+    uint64_t i;
+    int32_t *head0, *next0, *head40, *next40, *pt_list;
+    uint64_t n_pt = 0;
+    int have_va = 0;
+
+    if (argc < 3) {
+        fprintf(stderr, "usage: %s <ramfile> <target_pa> [va]\n", argv[0]);
+        return 2;
+    }
+    path = argv[1];
+    target_pa = strtoull(argv[2], NULL, 0) & PA_MASK;
+    if (argc >= 4) {
+        va = strtoull(argv[3], NULL, 0);
+        have_va = 1;
+    } else {
+        va = 0x4100000ULL;
+    }
+    /* indices: canonical 4-level split */
+    idx_pml4 = (unsigned)((va >> 39) & 0x1ff);
+    idx_pdpt = (unsigned)((va >> 30) & 0x1ff);
+    idx_pd   = (unsigned)((va >> 21) & 0x1ff);
+    idx_pt   = (unsigned)((va >> 12) & 0x1ff);
+
+    fd = open(path, O_RDONLY);
+    if (fd < 0) { perror("open"); return 1; }
+    if (fstat(fd, &st) < 0) { perror("fstat"); return 1; }
+    if (st.st_size == 0) { fprintf(stderr, "empty file\n"); return 1; }
+    n_pages = (uint64_t)st.st_size >> PAGE_SHIFT;
+
+    ram = mmap(NULL, (size_t)st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+    if (ram == MAP_FAILED) { perror("mmap"); return 1; }
+    madvise((void *)ram, (size_t)st.st_size, MADV_SEQUENTIAL);
+
+    fprintf(stderr, "ramfile=%s size=%llu bytes pages=%llu\n",
+            path, (unsigned long long)st.st_size, (unsigned long long)n_pages);
+    fprintf(stderr, "target_pa=0x%llx va=0x%llx idx: PML4[%u] PDPT[%u] PD[%u] PT[%u]\n",
+            (unsigned long long)target_pa, (unsigned long long)va,
+            idx_pml4, idx_pdpt, idx_pd, idx_pt);
+    fprintf(stderr, "PT entry offset=0x%x PD entry offset=0x%x\n",
+            idx_pt * 8, idx_pd * 8);
+
+    head0  = malloc(n_pages * sizeof(int32_t));
+    next0  = malloc(n_pages * sizeof(int32_t));
+    head40 = malloc(n_pages * sizeof(int32_t));
+    next40 = malloc(n_pages * sizeof(int32_t));
+    pt_list = malloc(n_pages * sizeof(int32_t));
+    if (!head0 || !next0 || !head40 || !next40 || !pt_list) {
+        fprintf(stderr, "out of memory\n"); return 1;
+    }
+    for (i = 0; i < n_pages; i++) { head0[i] = -1; head40[i] = -1; }
+
+    for (i = 0; i < n_pages; i++) {
+        const uint8_t *p = ram + (i << PAGE_SHIFT);
+        uint64_t e0, e40, ept, a;
+        memcpy(&e0,  p + 0x000, 8);
+        memcpy(&e40, p + 0x040, 8);
+        memcpy(&ept, p + (uint64_t)idx_pt * 8, 8);
+
+        if (entry_mask(ept) == target_pa)
+            pt_list[n_pt++] = (int32_t)i;
+
+        a = entry_mask(e0);
+        if (a < (n_pages << PAGE_SHIFT) && (a & (PAGE_SIZE - 1)) == 0) {
+            uint64_t j = a >> PAGE_SHIFT;
+            next0[i] = head0[j];
+            head0[j] = (int32_t)i;
+        }
+        a = entry_mask(e40);
+        if (a < (n_pages << PAGE_SHIFT) && (a & (PAGE_SIZE - 1)) == 0) {
+            uint64_t j = a >> PAGE_SHIFT;
+            next40[i] = head40[j];
+            head40[j] = (int32_t)i;
+        }
+    }
+    madvise((void *)ram, (size_t)st.st_size, MADV_RANDOM);
+
+    fprintf(stderr, "pages whose entry[0x%x] == target: %llu\n",
+            idx_pt * 8, (unsigned long long)n_pt);
+
+    uint64_t n_chain = 0;
+    for (uint64_t t = 0; t < n_pt; t++) {
+        int32_t pt = pt_list[t];
+        int32_t pd;
+        for (pd = head40[pt]; pd >= 0; pd = next40[pd]) {
+            int32_t pdpt;
+            for (pdpt = head0[pd]; pdpt >= 0; pdpt = next0[pdpt]) {
+                int32_t pml4;
+                for (pml4 = head0[pdpt]; pml4 >= 0; pml4 = next0[pml4]) {
+                    uint64_t pa_pml4 = (uint64_t)pml4 << PAGE_SHIFT;
+                    uint64_t pa_pdpt = (uint64_t)pdpt << PAGE_SHIFT;
+                    uint64_t pa_pd   = (uint64_t)pd   << PAGE_SHIFT;
+                    uint64_t pa_pt   = (uint64_t)pt   << PAGE_SHIFT;
+                    uint64_t raw[4] = {0}, fin;
+                    fin = walk4(pa_pml4, raw);
+                    n_chain++;
+                    printf("\n=== candidate #%llu ===\n", (unsigned long long)n_chain);
+                    printf("pdb (PML4 PA) = 0x%llx\n", (unsigned long long)pa_pml4);
+                    printf("PML4[%u]  @0x%llx+0x%03x = 0x%016llx -> PDPT 0x%llx  [%s]\n",
+                           idx_pml4, (unsigned long long)pa_pml4, idx_pml4 * 8,
+                           (unsigned long long)raw[0], (unsigned long long)pa_pdpt,
+                           bits(raw[0]));
+                    printf("PDPT[%u] @0x%llx+0x%03x = 0x%016llx -> PD   0x%llx  [%s]\n",
+                           idx_pdpt, (unsigned long long)pa_pdpt, idx_pdpt * 8,
+                           (unsigned long long)raw[1], (unsigned long long)pa_pd,
+                           bits(raw[1]));
+                    printf("PD[%u]   @0x%llx+0x%03x = 0x%016llx -> PT   0x%llx  [%s]\n",
+                           idx_pd, (unsigned long long)pa_pd, idx_pd * 8,
+                           (unsigned long long)raw[2], (unsigned long long)pa_pt,
+                           bits(raw[2]));
+                    printf("PT[%u]   @0x%llx+0x%03x = 0x%016llx -> PA   0x%llx  [%s]\n",
+                           idx_pt, (unsigned long long)pa_pt, idx_pt * 8,
+                           (unsigned long long)raw[3],
+                           (unsigned long long)entry_mask(raw[3]), bits(raw[3]));
+                    printf("walk_result = 0x%llx  %s\n",
+                           (unsigned long long)fin,
+                           fin == target_pa ? "MATCH" : "MISMATCH");
+                }
+            }
+        }
+    }
+
+    /* Reference: the caller-supplied known pdb, if present in the file. */
+    if (have_va) {
+        uint64_t known = 0x11092a000ULL;
+        if (known < (n_pages << PAGE_SHIFT)) {
+            uint64_t raw[4] = {0}, fin = walk4(known, raw);
+            printf("\n=== reference walk from known pdb 0x%llx ===\n",
+                   (unsigned long long)known);
+            printf("PML4[%u]=0x%016llx PDPT[%u]=0x%016llx PD[%u]=0x%016llx PT[%u]=0x%016llx\n",
+                   idx_pml4, (unsigned long long)raw[0],
+                   idx_pdpt, (unsigned long long)raw[1],
+                   idx_pd, (unsigned long long)raw[2],
+                   idx_pt, (unsigned long long)raw[3]);
+            printf("walk_result = 0x%llx\n", (unsigned long long)fin);
+        }
+    }
+
+    printf("\ntotal candidate chains: %llu\n", (unsigned long long)n_chain);
+
+    munmap((void *)ram, (size_t)st.st_size);
+    close(fd);
+    free(head0); free(next0); free(head40); free(next40); free(pt_list);
+    return 0;
+}